Method and apparatus for inspecting integrated circuit pattern

ABSTRACT

A circuit pattern inspection method and an apparatus therefor, in which the whole of a portion to be inspected of a sample to be inspected is made to be in a predetermined charged state, the portion to be inspected is irradiated with an image-forming high-density electron beam while scanning the electron beam, secondary charged particles are detected at a portion irradiated with the electron beam after a predetermined period of time from an instance when the electron beam is irradiated, an image is formed on the basis of the thus detected secondary charged particle signal, and the portion to be inspected is inspected by using the thus formed image.

This is a continuation application of U.S. Ser. No. 10/379,555, filedMar. 6, 2003 now U.S. Pat. No. 7,026,830; which is a continuationapplication of U.S. Ser. No. 09/983,703, filed Oct. 25, 2001, now U.S.Pat. No. 6,559,663; which is a continuation application of U.S. Ser. No.09/525,341, filed Mar. 14, 2000, now U.S. Pat. No. 6,329,826; which is acontinuation application of U.S. Ser. No. 08/811,511, filed Mar. 4,1997, now U.S. Pat. No. 6,172,363.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for producing asubstrate having a micro circuit pattern for a semiconductor device, aliquid crystal, or the like, and particularly relates to a technique forinspecting a pattern for a semiconductor device or a photomask, that is,the present invention relates to a technique for inspecting a pattern ona wafer in a way of semiconductor device producing process and atechnique for performing comparison and inspection by using an electronbeam.

Inspection of a semiconductor wafer will be described as an example.

A semiconductor device is produced by repeating a process oftransferring, by lithographing and etching, a pattern formed in aphotomask onto a semiconductor wafer. In a semiconductor deviceproducing process, the state of lithographing, etching, or the like,generation of particles, and so on, exert a large influence on the yieldof the semiconductor device. Accordingly, in order to detect occurrenceof abnormality or failure in an early stage or preparatorily,conventionally, a method of inspecting a pattern on a semiconductorwafer is carried out in a way of producing process.

As for a method of inspecting a defect existing in a pattern on asemiconductor wafer, a defect inspecting apparatus in which white lightis irradiated onto a semiconductor wafer so that circuit patterns of thesame kind in a plurality of LSIs are compared with each other by usingan optical image, has been put into practice. The outline of theinspecting method has been described in “Monthly Semiconductor World”,August issue, pp. 96-99, 1995. Further, as a inspecting method using anoptical image, a method in which an optically illuminated region on asubstrate is formed as an image by means of a time-delay integratingsensor so that the characteristic of the image is compared with designedcharacteristic inputted in advance to thereby detect a defect, has beendisclosed in JP-A-3-167456 or a method in which the deterioration of animage at the time of acquisition of the image is monitored so that thedeterioration of the image is corrected at the time of detection of theimage to thereby perform comparison and inspection in a stabler opticalimage, has been disclosed in JP-B-6-58220. If a semiconductor wafer in away of producing process was inspected by such an optical inspectionmethod, the pattern residue or defect having a light-transmissiblesilicon oxide film or a photoresist material on its surface could not bedetected. Further, an etching remainder or a incomplete-open failure ina micro conduct hole smaller than the resolution of an optical systemcould not be detected. Further, a defect generated in a wiring-patternstepped bottom portion could not be detected.

As described above, with the advance of reduction in size of the circuitpattern and complication in shape of the circuit pattern and with theadvance of diversification of the material, it has become difficult todetect a defect by using an optical image. Therefore, a method forcomparing and inspecting a circuit pattern by using an electron beamimage having higher resolution than that of the optical image has beenproposed. When a circuit pattern is compared and inspected by means ofan electron beam image, in order to obtain a practical inspection time,the image needs to be acquired at a very high speed in comparison withobservation by using a scanning electron microscopy (hereinafterabbreviated to SEM). Further, it is necessary to secure resolution andan SN ratio in the image acquired at a high speed.

As a pattern comparison and inspection apparatus using an electron beam,a method in which an electron beam with an electron-beam current notsmaller than 100 times (10 nA) as large as the current in the generalSEM is irradiated onto an electrically conductive substrate (such as anX-ray mask, or the like) to detect any electrons among secondaryelectrons, reflected electrons and transmitted electrons generatedtherefrom and compare/inspect an image formed from a signal of theelectrons to thereby automatically detect a defect is disclosed in J.Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991), J. Vac. Sci.Tech. B, Vol. 10, No. 6, pp. 2804-2808 (1992), JP-A-5-258703 and U.S.Pat. No. 5,502,306.

Further, as a method for inspecting or observing a circuit substratehaving an insulating material by means of an electron beam, a method inwhich a stabler image is acquired by irradiation of a low-acceleratedelectron beam not higher than 2 keV in order to reduce the influence ofcharge has been disclosed in JP-A-59-155941 and “Electron and Ion BeamsHandbook” (THE NIKKAN KOGYO SHINBUN, Ltd.), pp. 622-623. Further, amethod in which ions are irradiated from the back of a semiconductorsubstrate has been disclosed in JP-A-2-15546 and a method in which lightis irradiated onto a surface of a semiconductor substrate to therebycancel charge of an insulating material is disclosed in JP-A-6-338280.

Further, in a large-current and low-accelerated electron beam, it isdifficult to acquire a high-resolution image because of a space-chargeeffect. As a measure to solve this problem, a method in which ahigh-accelerated electron beam is retarded just before a sample so thata substantially low-accelerated electron beam is irradiated onto thesample is disclosed in JP-A-5-258703.

As a method for acquiring an electron-beam image at a high speed, amethod in which an image is acquired by continuously irradiating anelectron beam onto a semiconductor wafer on a sample stage whilecontinuously moving the sample stage is disclosed in JP-A-59-160948 andJP-A-5-258703. Further, a structure constituted by a scintillator(Al-vapor deposited fluorescent material), a light guide and aphoto-multiplier is used as a secondary electron detecting apparatusused conventionally in the SEM. A detecting apparatus of this type is,however, poor in frequency responsibility because light emission fromthe fluorescent material is detected, so that the detecting apparatus ofthis type is unsuitable for formation of an electron beam image at ahigh speed. As a detecting apparatus for detecting a high-frequencysecondary electron signal to solve this problem, a detection means usinga semiconductor detector is disclosed in JP-A-5-258703.

When a circuit pattern in a process for producing a micro-structuresemiconductor device was detected by using the aforementioned prior artoptical inspection method, it was possible to detect the residue of asilicon oxide film, a resist material, or the like, which was formedfrom an optically transmissible material and which was sufficientlyshort in the optical distance depending on the optical wavelength andrefractive index used for inspection, and it was difficult to detect anetching remainder or a incomplete-open failure in a micro conduct holewhich was linear so that the width of a short side thereof was notlarger than the resolution of an optical system.

On the other hand, in the observation and inspection using the SEM,there are two problems as follows. One problem is that a very long timeis required for inspecting a circuit pattern on the whole surface of asemiconductor wafer because the conventional method, by means of theSEM, for forming an electron-beam image needs a very long time.Accordingly, in order to obtain practical throughput in a semiconductordevice producing process, or the like, it was necessary to acquire anelectron-beam image at a very high speed. It was further necessary tosecure the SN ratio of the electron-beam image acquired at a high speedand to keep accuracy in a predetermined value.

The other problem was that it was difficult to obtain a stable contrastimage in inspection by means of an electron beam and to obtain apredetermined value of inspection accuracy in the case where thematerial constituting a circuit pattern as a subject to be inspected wasformed from an electrically insulating material such as a resist, asilicon oxide film, or the like, or in the case where the material wasformed from a mixture of an electrically insulating material and anelectrically conducting material. This is because, when an electron beamis irradiated onto a matter, secondary electrons are generated from theirradiated portion of the material but the matter is charged because theirradiated current value is not equal to the secondary electron currentvalue in the case where the subject to be inspected is an electricallyinsulating material. When charge occurs, efficiency in generation ofsecondary electrons from that charged portion and the orbit of secondaryelectrons after the generation are influenced so that not only thecontrast of the image is changed but also the image is distorted withoutreflection of the actual shape of the circuit pattern. This charge stateis sensitive to the condition of electron-beam irradiation, so that ifthe speed or range of irradiation of the electron beam is changed, animage quite different in contrast is obtained even in one and the sameposition and even in one and the same circuit pattern.

In order to detect a defect being unable to be detected by an opticalinspection method with respect to the prior art, a method in whichinspection is carried out by irradiating a narrowed electron beam onto asample substrate at a high speed is disclosed in JP-A-59-160948 andJP-A-5-258703 as a method for performing comparison and inspection bymeans of an electron-beam image acquired by irradiating an electron beamonto an electrically conductive substrate. In this conventionaltechnique, however, there is no description about a method for adjustingthe inspection condition with respect to a material such as anelectrically insulating material, or the like. Further, as anotherconventional technique, a method in which a primary electron beam to beirradiated onto a sample substrate is retarded to thereby makeirradiation energy low-accelerated, for example, not higher than 2 keV,in order to observe a substrate having an electrically insulatingmaterial is described in JP-A-59-155941. This conventional technique is,however, a method in which an electron beam is continuously irradiatedonto a certain local region so that an image is acquired after thecharge of the local region becomes stable. Accordingly, thisconventional technique is unsuitable for inspecting a wide region at ahigh speed because a long time is required for acquiring theelectron-beam image. Further, even in the case where charge in the localregion is stable, it is difficult that another region to be compared iscontrolled to be in the same charge state. For example, it is difficultto inspect a wide region of a semiconductor wafer, or the like.

In the case where not only a converged electron beam small inelectron-beam current is slowly irradiated onto a sample but also a longtime is taken for signal detection as shown in the conventional SEM, asignal detected in a detection time per unit pixel is integrated to forman image signal of the unit pixel so that an SN ratio necessary forcomparison and inspection is obtained. Because the state of chargechanges with the passage of time correspondingly to the irradiation timeas described above, the image signal changes during integration so thatit is difficult to obtain stable contrast. The present inventors havefound that, as a method for inspecting a circuit substrate having suchan electrically insulating material, it is effective for obtainingstable contrast to shorten the secondary electron signal detection timeto thereby eliminate the contrast fluctuation due to the aforementionedprocess such as integration, or the like, and to thereby suppress theinfluence on the change of charge with the passage of time. Further, thepresent inventors have found that an electron-beam image of contrast dueto the secondary electron generation efficiency of the material of thesample by irradiating a large probe sized electron beam in a range offrom about 10 nm to about 50 nm onto a sample at a high speed to acquirean image instantaneously is more suitable than an electron-beam imagebased on contour information of a shape acquired by an electron beamconverged to a range of from 5 nm to 10 nm as shown in the SEM of theconventional technique. As described above, a theme of the presentinvention is not only to acquire an electron-beam image of contrastgenerated from a material instantaneously by scanning a large probesized electron beam at a high speed in comparison with the conventionaltechnique but also to secure the SN ratio or resolution in theelectron-beam image sufficiently adapted for image comparison andinspection.

In order to radiate an electron beam at a high speed, detect a signal ata high speed and secure the SN ratio and resolution in the electron-beamimage as described above, an electron beam having an electron-beamcurrent larger than that generally used in the SEM needs to beirradiated onto a substrate to be inspected as described in the priorart. As described in the prior art, with a large-current andlow-accelerated electron beam, it is difficult to obtain an image ofhigh resolution because of the space-charge effect. As a method to solvethis problem, there is a method in which a high-accelerated electronbeam is retarded just before a sample so that a substantiallylow-accelerated electron beam is irradiated onto the sample. In order tocarry out the deceleration of the primary electron beam, a negativevoltage for deceleration is required to be applied to a samplesubstrate, a sample stage, or the like. When the primary electron beamretarded by the negative voltage is irradiated onto the samplesubstrate, secondary electrons having energy of the order of tens of mVare generated from a surface of the substrate. Because an electric fieldgenerated by the negative voltage for deceleration acts on the secondaryelectrons to accelerate the secondary electrons to energy of the orderof kV, it is difficult to collect the high-speed secondary electrons toa detector. As a method for collecting secondary electrons to adetector, there has been proposed, in the prior art, a method using adeflector (hereinafter referred to as ExB deflector) for offsetting thequantities of deflection caused by the electric field and magnetic fieldacting on the primary electron beam and for deflecting secondaryelectrons by superposing the quantities of deflection on each other. Inthe case where the detector is located in a place away from the orbit ofthe primary electron beam, however, the secondary electrons need to bedeflected largely by the aforementioned ExB deflector in order tocollect the secondary electrons to the detector. If the quantity ofdeflection is selected to be too large, there arises a problem that thesecondary electrons collide with a deflection plate per se of the ExBdeflector so that the secondary electrons cannot be led to the detector.Further, if the deflection by the ExB deflector is selected to beintensive, there arises a problem that aberration occurs in the primaryelectron beam so that it is difficult to converge the electron beam on asurface of the sample substrate through an objective lens, or the like.

Further, as described in the prior art, in order to form anelectron-beam image at a high speed, a detection means using asemiconductor detector is used as a detection apparatus for detecting ahigh-frequency secondary electron signal. This prior art means comprisesa semiconductor detector reversely biased and high in response speed, apreamplifier for amplifying an analog signal detected by thesemiconductor detector, and means for light-transmitting the analogsignal amplified by the preamplifier. The aforementioned semiconductordetector and the aforementioned preamplifier are floated to a positivehigh electric potential. In this conventional method, the analog signaldetected by the semiconductor detector is transmitted as it is by thelight-transmitting means. This light-transmitting means, however, isconstituted by a light-emitting element for converting an electricsignal into a light signal, an optical fiber cable, and alight-receiving element for converting a light signal into an electricsignal. Accordingly, there arises a problem that noise generated fromthe light-emitting element and the light-receiving element is added tothe original analog signal to lower the SN ratio in the secondaryelectron signal.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide an inspectiontechnique in which a circuit pattern which is hardly detected on thebasis of an optical image and is formed from a material havingelectrically insulating property or a circuit pattern which is formedfrom a mixture of a material having electrically insulating property anda material having an electrically conducting property can be inspectedby using an electron-beam image.

A second object of the present invention is to acquire an electron-beamimage as a good-quality image which is high in the speed, good in thestability, high in the resolution, high in the contrast and large in theSN ratio in order to perform inspection by using the aforementionedelectron-beam image so that a defect generated on a micro circuitpattern can be detected accurately in comparison and inspection.

A third object of the present invention is to provide a technique inwhich a large-current relatively large probe sized electron beam isirradiated onto a sample at a high speed and generated secondaryelectrons are detected instantaneously and efficiently so that anelectron-beam image of high contrast generated from the material of thesample is formed in a condition corresponding to the material of thesample to thereby acquire a stable electron-beam image also with respectto the electrically insulating material.

A fourth object of the present invention is to provide means forefficiently detecting secondary electrons generated by irradiation of anelectron beam onto a sample or for detecting high-speed high-frequencysecondary electrons with a high SN ratio to thereby achieve theaforementioned first, second and third objects.

A fifth object of the present invention is to provide a technique forinspecting a circuit pattern with high accuracy to achieve theaforementioned first through fourth objects, that is, to provide aninspection method in which the inspection is applied to a semiconductordevice or other micro circuit patterns so that a result of theinspection is reflected on the condition for producing the semiconductordevice, or the like, to thereby bring contribution not only toimprovement in reliability of the semiconductor device, or the like, butalso to reduction in the level of defectiveness.

A substrate having a micro circuit pattern such as a semiconductordevice or the like may be formed not only from an electricallyconductive film singly but also from an electrically conductive film andan electrically insulating material. In order to achieve theaforementioned objects for irradiating an electron beam onto a circuitpattern having an electrically insulating material to thereby detect amicro defect on a micro pattern at a high speed, a method and apparatusfor inspecting a circuit pattern according to the present invention willbe described below.

According to the present inventors' discussion, it has been found thatcontrast changes largely in accordance with time and position when alarge quantity of electron beams are unevenly irradiated onto a localregion of a substrate surface containing an electrically insulatingmaterial but an electron-beam image of stable contrast can be obtainedeven in the electrically insulating material when an electron beamhaving an electric potential substantially equal to that in theperiphery of a region to be inspected in the substrate is evenlyirradiated onto the sample in the region to be inspected so thatsecondary electrons generated in a very short time are detected. This isbecause a signal little in the fluctuation of incidence of secondaryelectrons with the passage of time can be acquired by detectingsecondary electrons instantaneously in a very short time even in atransitional period in which the sample is charged by the irradiation ofthe electron beam. Further, the present inventors have found that anelectron-beam image of contrast generated by the secondary electrongenerating efficiency in the material of the sample by irradiation of alarge probe sized electron beam in a range of from about 50 nm to about100 nm onto the sample at a high speed to acquire an imageinstantaneously is more suitable for detection of a defect than anelectron-beam image based on contour information of a shape acquired bya converged electron beam in a range of from 5 nm to 10 nm asrepresented by the SEM in the prior art. The secondary electrongenerating efficiency varies in accordance with the material of asub-layer which forms a circuit pattern therein, the material of asurface pattern and the thickness of the film. Accordingly, if anelectron-beam image of high contrast in the pattern and the subbinglayer is acquired, a defect in the pattern generated by the material ora defect in the sub-layer can be detected easily. The secondary electrongenerating efficiency in each material constituting the circuit patternvaries in accordance with the condition for irradiation of an electronbeam. The secondary electron generating efficiency varies also inaccordance with the state of charge. Therefore, if the condition ofirradiation or the condition of charge is optimized in accordance withthe material so that the contrast due to the surface pattern and thesub-layer material becomes high, an electron-beam image suitable fordetection of each defect can be formed in accordance with thecombination of materials. To this end, therefore, there are a method inwhich secondary electrons generated by irradiating an electron beam onceare detected in a very short time to thereby form an electron-beamimage, and a method in which secondary electrons generated in a state inwhich the contrast is increased by irradiation of an electron beamseveral times in accordance with the material are detected in a veryshort time. Further, it has been found that there are a method in whichan electron-beam image is obtained by irradiating an electron beam onceor several times at a high speed and detecting secondary electrons in avery short time in a period in which the transitional change of anelectric potential due to the charge is little, and a method in which anelectron-beam image is obtained by irradiating an electron beam or othercharged-particle beam onto a sample substrate in advance in accordancewith the combination of materials and detecting secondary electrons in avery short time after the state of charge is stabilized and the contrastbecomes high. Because, in any method, an electron beam is irradiatedevenly onto a region to be inspected in a state in which the potentialof the region to be inspected in the substrate is substantially equal tothe potential of the periphery of the region, that is, in a state inwhich the charge is even, the contrast of the acquired image becomessubstantially even between different regions to be inspected.Accordingly, when electron-beam images are compared and inspected, nofalse detection is caused by the fluctuation of the contrast.

It has been found that a method in which a large-current electron beamis evenly and speedily irradiated onto a substrate to be inspected and asecondary electron signal corresponding to the region of beamirradiation is instantaneously detected simultaneously with theirradiation is effective to achieve the former detection method. Becausean electron beam is evenly instantaneously irradiated onto all regionsto be inspected at the time of inspection, the potential of thesubstrate due to the charge is even in that instance. Accordingly, theinfluence of the transitional change of charge with the passage of timecan be avoided when secondary electrons are detected instantaneously inthat state. Further, because the number of electrons incident to asample different in accordance with the material, to the number ofsecondary electrons emitted from the sample can be set to besubstantially equal if the energy of the electron beam irradiated ontothe sample is controlled, the contrast can be stabilized and the injuryof the sample circuit substrate can be avoided. That is, even in acircuit pattern having an electrically insulating material, an imagestable in contrast can be formed. The energy of the electron beamirradiated onto the sample can be controlled because the degree ofdeceleration can be changed by applying a negative potential to thesample or sample stage to retard the primary electron beam just abovethe sample and controlling the applied voltage to be variable.

As means for automatically inspecting a defect generated in a surface ofa circuit pattern of a semiconductor wafer, or the like, at a highspeed, secondary electrons are detected in a real time of the movementof the sample stage to form an image by scanning an electron beam at ahigh speed in a direction perpendicular to the direction of the movementof the sample stage while continuously moving the sample stage in onedirection, and the thus formed image is compared and inspected. In orderto achieve this inspection method, an electron beam is irradiated onceor several times at a high speed to form an image though the conditionfor irradiation of the electron beam varies in accordance with thematerial. The image quality of the electron-beam image adapted forcomparison and inspection by irradiation of the electron beam once orseveral times can be secured by the following four means. The firstmeans is to radiate a high-density electron beam onto a sample tothereby secure an SN ratio in a secondary electron signal as a base ofan electron-beam image necessary for inspection. Inspection is carriedout by using an electron beam with a current value not lower than 270pA, preferably, not lower than 13 nA. This current value is achieved bysetting the root of the number of irradiated electrons to besufficiently larger than the SN ratio in the electron-beam imagenecessary for inspection. The second means is to converge the electronbeam so that the diameter of the electron beam on the sample becomessufficiently small at the time of irradiation of a large-currentelectron beam onto the sample to thereby secure the resolution necessaryfor the inspection of a micro circuit pattern. As described in the priorart, in the observation of, by means of an electron beam, asemiconductor, or the like, having an electrically insulating material,the energy of the electron beam irradiated onto the sample is preferablyselected to be low-accelerated. In a large-current and low-acceleratedelectron beam, aberration caused by the space-charge effect occurs sothat it becomes difficult to converge the electron beam on the sample.Therefore, this problem can be solved by using the same method asdescribed above with respect to the means for controlling the energy ofthe electron beam irradiated onto the sample. That is, the space-chargeeffect can be suppressed by generating a high-accelerated electron beamfrom an electron source, and the diameter of the electron beam on thesample can be converged to secure required resolution by applying anegative potential to a sample or sample stage to retard thehigh-accelerated electron beam just before the sample and radiate anelectron beam of substantially optimum low-accelerated energy onto thesample. The third means is to efficiently lead secondary electronsgenerated from a surface to a detector to thereby secure the SN ratio ofthe electron-beam image necessary for inspection. When an electron beamis irradiated onto a sample by the second means, secondary electronsgenerated from the sample are contrariwise accelerated by the electricfield of a negative potential for decelerating the primary electronbeam. The accelerated secondary electrons are deflected by the ExBdeflector so as to be led to the detector. By deflecting the secondaryelectrons to radiate the secondary electrons onto a metal piece providedbetween the light path of the primary electron beam and the detector,and further leading the low-speed secondary electrons generated from themetal piece to the detector, the quantity of deflection can be reducedwithout any necessity of deflecting high-speed secondary electronslargely toward the detector. By this measure, the problem which occurswhen high-speed secondary electrons are deflected largely, that is, theproblem of the loss of secondary electrons caused by the collision ofsecondary electrons with the deflector, the lowering of resolutioncaused by the influence on the primary electron beam, and so on, can besolved. Furthermore, by using a material high in secondary electrongenerating efficiency as the metal piece, a larger number of secondaryelectrons than the number of electrons in the primary electron beam canbe obtained and, consequently, the SN ratio in the image can beimproved. The fourth means is to digitize an analog signal detected by asemiconductor detector which is used as a detector for forming an imagewith a high SN ratio at a high speed and to transmit the thus digitizedsignal. There is further provided means for converting the digitizedsignal into a light signal, transmitting the light signal by means of anoptical fiber, or the like, and converting the transmitted signal intoan electric signal again. The constituent elements from thesemiconductor detector to the photo-conversion means are floated at apositive potential. Thus, the analog signal detected by thesemiconductor detector is subjected to light transmission after it isdigitized by an AD converter. By use of the semiconductor detector, theresponsibility necessary for detecting secondary electrons at a highspeed can be secured. By digitized signal light-transmission, noise canbe suppressed because digital discrimination between 1 and 0 is neverinfluenced by noise even in the case where more or less noise isgenerated in a light-emitting element or in a light-receiving element inthe photoelectric conversion means. Further, by making the elements fromthe semiconductor detector to the photo-conversion means float at apositive potential, secondary electrons can be led into thesemiconductor detector so that circuits after the photo-conversion meanscan be operated at the ground potential. Accordingly, secondaryelectrons generated from a sample by irradiation of an electron beamonto the sample can be detected at a high speed with little influence ofnoise.

By the aforementioned various means, a stable image can be obtained withrespect to a circuit pattern having an electrically insulating materialin a condition in which the fluctuation of image contrast caused bycharge is suppressed, so that a high sensitivity, high speed and high SNratio electron-beam image can be formed.

Of the two means, that is, a method which is effective for inspecting anaforementioned circuit pattern having an electrically insulatingmaterial and in which an electron beam is irradiated once or severaltimes at a high speed so that an electron-beam image is obtained beforeoccurrence of the change of a potential due to charge, and a method inwhich an electron beam or other charge particle beam is irradiated sothat an electron-beam image is obtained after the state of charge isstabilized, the former has been described. Means for the latterinspection method will be described below.

To stabilize the state of charge before inspection in the latter method,there are two means. The first means is a method in which a secondcharge particle beam such as an electron beam, an ion beam, plasma, anelectron shower, or the like, is irradiated in advance onto a substrateto be inspected, in a sub chamber, or the like, different from a chamberused for inspection so as to charge the substrate to a positive ornegative potential before inspection. The second means is to radiate asecond electron beam onto a substrate to be inspected, in a state inwhich the substrate is carried to a chamber for inspection and placed ina position for forming an inspection image. In order to radiate thesecond electron beam onto the region to be inspected before inspectionwithout influence on inspection:

(1) the time of irradiation of the first electron beam for forming aninspection image and the time of irradiation of the second electron beamare shifted from each other;

(2) the first electron beam for forming an inspection image is subjectto raster-scanning on the substrate to be inspected whereas the secondelectron beam is irradiated in a period in which the first electron beamturns back in the scanning; (3) the first electron beam for forming aninspection image and the second electron beam are coaxiallysimultaneously irradiated onto a substrate to be inspected so that notonly the diameter of the second electron beam is sufficiently largerthan that of the first electron beam but also the maximum currentdensity of the second electron beam is sufficiently smaller than themaximum current density of the first electron beam. As for theconfiguration thereof, one second electron beam source or a plurality ofsecond electron beam sources may be disposed in the peripheral portionof an opening through which the first electron beam for forming aninspection image is irradiated so that not only the respective secondelectron beam sources operate independently but also each secondelectron beam is irradiated onto a region to be inspected in a substrateto be inspected before the first electron beam is irradiated.

As means for irradiating the second charge particle beam by a methodother than the aforementioned methods, the charge particle beam may bean ion beam and an ion source is provided in the peripheral portion ofthe opening through which the first electron beam for forming aninspection image is irradiated so that the ion beam is irradiated ontothe substrate to be inspected at the time of inspection of the subjectto be inspected. As for the timing of irradiation, there is no problemwhen the time of irradiation of the first electron beam and the time ofirradiation of the ion beam are staggered in the same manner as in thecase where the second charge particle beam is an electron beam or whenthe ion beam is irradiated in a period in which the scanning of thefirst electron beam turns back.

By the aforementioned means, an electron-beam image for a circuitpattern having an electrically insulating material can be formed in analways stable state of charge by irradiating the first electron beam forforming an inspection image after irradiating the second charge particlebeam onto a substrate to be inspected to make the state of charge in asurface of the substrate uniform. According to the electricallyinsulating material, the contrast between the electrically insulatingmaterial and the sub-layer may be increased when the substrate ischarged. In this case, the method of irradiating the second chargeparticle beam according to the present invention becomes effectivebecause sufficient contrast for comparison and inspection cannot beobtained though the fluctuation of the electron-beam image caused bycharge can be suppressed when only the condition for irradiation of thefirst electron beam for forming an inspection image is controlled.

In the aforementioned means for forming an electron-beam image afterstabilizing the state of charge in a surface of the substrate to beinspected by the second charge particle beam, the condition and meansfor irradiation of the first electron beam are the same as in the meansfor irradiating the first electron beam once or several times so that animage is formed before the change caused by charge occurs. Further,means for performing inspection at a high speed and means for making theimage quality of the electron-beam image have a high SN ratio and a highresolution at the time of high-speed inspection are the same as in theaforementioned means. Further, in the means for forming an electron-beamimage for inspection by the first electron beam after irradiating thesecond charge particle beam to stabilize charge, means for adjusting thestate of charge can be used additionally by controlling the irradiationenergy of the first electron beam and second charge particle beamirradiated onto the sample. In the case where a charge particle beamother than the electron beam for forming an image is irradiatedsimultaneously or nearly simultaneously with the irradiation of theelectron beam, there is a possibility that a secondary electron signalunnecessary for forming the original image may be generated anddetected. In this case, an aperture is placed on an image plane of thesurface of the substrate on which forms an image of a circuit pattern ofa substrate to be inspected by secondary electrons, so that only thesecondary electrons generated from the region subjected to irradiationof the electron beam for forming an inspection image can be passedthrough the aperture and led to the secondary electron detector tothereby eliminate unnecessary secondary electrons.

Among the means for inspecting a substrate having a micro circuitpattern by an electron beam, various means for forming an electron-beamimage have been described above. Means for detecting a defect generatedon a circuit pattern on the basis of an electron-beam image will bedescribed below. Secondary electrons generated from a surface of asample by irradiating a first electron beam onto a first region of thesample is detected at a high speed and with high efficiency,

so that an image signal of the electron beam from the first region ofthe substrate to be inspected is obtained and stored in a first storageportion. In this occasion, if necessary, a second charge particle beamis irradiated before the irradiation of the first electron beam.Similarly, an electron-beam image of a region which is a second regionof the sample and which has the same circuit pattern as that of thefirst region is obtained. After detailed position adjustment withrespect to images of the first and second regions is carried out in animage processing portion while the electron-beam image of the secondregion is stored in a second storage portion, a differential image isobtained by comparison between the images of the first and secondregions. A pixel in which the absolute value of the brightness of thedifferential image is not smaller than a predetermined threshold isdetermined to be a candidate for a defect. In another means, anelectron-beam image of a good-quality circuit pattern different fromthat of the substrate to be inspected is formed in a redeterminedcondition and stored in the first storage portion in advance. The firstregion of the substrate to be inspected is irradiated with a firstelectron beam and the secondary electrons generated from a surface ofthe sample is detected at a high speed and with high efficiency tothereby obtain an electron-beam image signal of the first region of thesubstrate to be inspected. The image is compared with the image of thegood-quality circuit pattern stored in the first storage region, and aprocessing is performed such that the inspection image is determined asa defect when the absolute value of the brightness of the differentialimage is larger than a predetermined threshold. Also in this occasion,if necessary, a second charge particle beam is irradiated before theirradiation of the first electron beam. Further, because an image isformed by irradiating the first electron beam once or several times ontoeach of the first and second regions of the substrate to be inspected,as means for preventing the electron beam from being irradiated ontoregions other than the image-forming region, a monitor for adjusting thefocal position of the first electron beam is irradiated always with abeam such as white light other than the electron beam and reflected highis monitored. Alternatively, the region to be inspected in the substrateto be inspected can be prevented from being charged locally and thecause of false detection can be eliminated by means in which anelectron-beam image is acquired in a region other than the region to beinspected and the region to be inspected is managed so that inspectionis always carried out by the irradiation of the electron beam in thefirst cycle when the condition for sensitivity and the condition forirradiation of the electron beam are set in accordance with thesubstrate to be inspected before inspection.

By carrying out the aforementioned inspection method, it is possible torealize a method and apparatus for inspection, in which a circuitpattern on a substrate containing an electrically insulating material isinspected at a high speed with high sensitivity by an electron beam sothat a defect generated on the circuit pattern can be detectedautomatically.

By inspecting a substrate having a circuit pattern, for example, such asa semiconductor device in a way of

producing process by using this method and apparatus, a failure ordefect which is generated in the shape of the pattern by a process andwhich could not be detected in a semiconductor device in every step bythe conventional technique, can be detected in an early stage. As aresult, problems which are latent in processes, production apparatusconditions, and so on, can be actualized. Accordingly, a countermeasureagainst the cause of failure in high-speed high-accurate processes ofproducing various kinds of substrates such as semiconductor devicescompared with the conventional processes can be taken. Accordingly, notonly a high yield, that is, a high efficiency percentage can be securedbut also high accurate inspection can be made because error detectionwhich occurs in inspection and becomes a problem is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the configuration of a circuit patterninspection apparatus;

FIG. 2 is a view showing the configuration of a main part of aelectronic optical system and a secondary electron detection portion;

FIGS. 3( a), 3(b) and 3(c) are views showing correlation betweenelectron beam irradiation, sample charge and secondary electrongeneration;

FIGS. 4( a) and 4(b) are views for explaining the influence of thecondition of electron beam irradiation on the contrast;

FIGS. 5( a) and 5(b) are views for explaining a electron scanningmethod;

FIG. 6 is a view for explaining a flow of a semiconductor deviceproducing process;

FIGS. 7( a) and 7(b) are views for explaining a semiconductor devicecircuit pattern and a content of defect;

FIG. 8 is a view showing the configuration of a main part of theelectronic optical system of a third embodiment;

FIG. 9 is a view showing the configuration of an enlarged part of theelectric optical system of a fourth embodiment;

FIG. 10 is a view showing the configuration of the circuit patterninspection apparatus of a fifth embodiment;

FIGS. 11(a) and 11(b) are views for explaining the influence of theelectron beam irradiation time on the contrast;

FIG. 12 is a view showing the configuration of a main part of theinspection apparatus of a sixth embodiment;

FIG. 13 is a view for explaining the principle of the deflector of thesixth embodiment;

FIGS. 14( a) and 14(b) are views for explaining the shape of theelectron beam of the sixth embodiment;

FIGS. 15( a) and 15(b) are views showing the configuration of a mainpart of the electronic optical system of a seventh embodiment;

FIG. 16 is a view showing the operation of the seventh embodiment; and

FIG. 17 is a view showing the configuration of a main part of theinspection apparatus of an eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention as to an example of the inspectionmethod and apparatus will be described below in detail with reference tothe drawings.

Embodiment 1

FIG. 1 shows the configuration of a circuit pattern inspection apparatus1 according to a first embodiment of the present invention. The circuitpattern inspection apparatus 1 has an inspection chamber 2 to beevacuated, and a sub chamber (not shown in this embodiment) for carryinga sample substrate 9 into the inspection chamber 2. The sub chamber isconfigured so as to be able to be evacuated independently of theinspection chamber 2. The circuit pattern inspection apparatus 1 isconstituted by a control portion 6, an image processing portion 5 inaddition to the inspection chamber 2 and the sub chamber. The inside ofthe inspection chamber 2 is roughly constituted by an electronic opticalsystem 3, a secondary electron detection portion 7, a sample chamber 8,and an optical microscope portion 4. The electronic optical system 3 hasan electron gun 10, an electron beam extracting electrode 11, acondenser lens 12, a blanking deflector 13, a scanning deflector 15, anaperture 14, an objective lens 16, a reflection plate 17, and an ExBdeflector 18. The secondary electron detection portion 7 has a secondaryelectron detector 20 which is disposed above the objective lens 16 inthe inspection chamber 2. The output signal of the secondary electrondetector 20 is amplified by a preamplifier 21 disposed in the outside ofthe inspection chamber 2 and is converted into digital data by an ADconverter 22. The sample chamber 8 is constituted by a sample stage 30,an X stage 31, a Y stage 32, a rotation stage 33, a position monitoringmeasuring device 34, and an inspection-subject substrate heightmeasuring device 35. The optical microscope portion 4 is disposed nearthe electronic optical system 3 in the inspection chamber 2 but at adistance from the electronic optical system 3 so that the two have noinfluence on each other. The distance between the electronic opticalsystem 3 and the optical microscope portion 4 is known. Further, the Xstage 31 or Y stage 32 is designed so as to make a reciprocating motionat the known distance between the electronic optical system 3 and theoptical microscope portion 4. The optical microscope portion 4 isconstituted by a light source 40, an optical lens 41, and a CCD camera42. The image processing portion 5 is constituted by a first imagestorage portion 46, a second image storage portion 47, an arithmeticoperation portion 48, and a defect judgment portion 49. An electron-beamimage or optical image taken in is displayed on a monitor 50.Instructions and conditions for operating respective portions of theapparatus are inputted/outputted through the control portion 6.Conditions such as the accelerated voltage at the time of generation ofan electron beam, the electron-beam deflection width, the deflectionspeed, the signal fetch timing of the secondary electron detector, themoving speed of the sample stage, etc. are inputted into the controlportion 6 in advance so as to be able to be set freely or selectively inaccordance with the purpose. The control portion 6 uses a positioncorrect control circuit 43 to monitor positional or height displacementfrom signals of the position monitoring measuring device 34 and theinspection-subject substrate height measuring device 35, generatecorrect signals from results thereof and feed the correct signals to theobjective lens source 45 and the scanning deflector 44 so that theelectron beam is irradiated onto an always correct position.

In order to acquire an image of the inspection-subject substrate 9,secondary electrons 51 generated by irradiating a converged electronbeam 19 onto the inspection-subject substrate 9 are detected insynchronism with the scanning of the electron beam 19 and the movementof the stages 31 and 32 to thereby obtain an image of a surface of theinspection-subject substrate 9. As described above in the Summary of theInvention, a high inspection speed is essential to the automaticinspection in the present invention. Accordingly, low-speed scanning ofan electron beam having an electron beam current of the order of pA asused in the general SEM or multiple repetition of scanning andsuperposition of respective images is not performed. Further, in orderto suppress the charge of an electrically insulating material, it isnecessary that electron-beam scanning is made at a high speed once orrepeated several times. Therefore, this embodiment is configured so thatan image is formed by only once scanning an electron beam with a largecurrent, for example, of 100 nA which is not smaller than about 100times as large as the current in the general SEM. The scanning width isselected to be 100 μm and one pixel is selected to be 0.1 μm so that onescanning is performed in 1 μs.

A diffusion supply type thermal field emission electron source is usedin the electron gun 10. An electron-beam image little in the change ofbrightness is obtained by using this electron gun 10 because a stableelectron-beam current can be secured, for example, in comparison with aconventional tungsten (W) filament electron source or field-freeemission type electron source. Further, high-speed inspection as will bedescribed later can be realized because the electron-beam current can beselected to be large by this electron gun 10. An electron beam 19 isextracted from the electron gun 10 by applying a voltage between theelectron gun 10 and the extraction electrode 11. Acceleration of theelectron beam 19 is performed by applying a high-voltage negativepotential to the electron gun 10. As a result, the electron beam 19 isirradiated toward the sample stage 30 by energy corresponding to thepotential, converged by the condenser lens 12, and the objective lens 16and then irradiated onto the inspection-subject substrate 9 (a microcircuit pattern-containing substrate such as a semiconductor wafer, asemiconductor chip, a liquid crystal, a mask, or the like) mounted onthe X-Y stages 31 and 32 on the sample stage 30. Incidentally, a signalgenerator 44 for generating a scanning signal and a blanking signal isconnected to the blanking deflector 13 and lens electric sources 45 areconnected to the condenser lens 12 and the objective lens 16respectively. It is designed so that a negative voltage can be appliedto the inspection-subject substrate 9 by a high-voltage electric source36. The primary electron beam is retarded by adjusting the voltage ofthis high-voltage electric source 36 so that the irradiation energy ofthe electron beam onto the inspection-subject substrate 9 can beadjusted to an optimum value without any change of the potential of theelectron gun 10.

Secondary electrons 51 generated by irradiation of the electron beam 19onto the inspection-subject substrate 9 are accelerated by a negativevoltage applied to the substrate 9. The accelerated secondary electrons51 are deflected to a predetermined direction by the ExB deflector 18which is disposed above the inspection-subject substrate 9. The quantityof deflection can be adjusted in accordance with the voltage and theintensity of magnetic field applied to the ExB deflector 18. Further,this electro-magnetic field can be changed so as to be interlocked withthe negative voltage applied to the sample. The secondary electrons 51deflected by the ExB deflector 18 collide with the reflection plate 17in a predetermined condition. This reflection plate 17 is united with ashield pipe of a deflector for an electron beam irradiated onto thesample (hereinafter referred to as primary electron beam) so as to beshaped like a cone. When the accelerated secondary electrons 51 collidewith this reflection plate 17, second secondary electrons 52 havingenergy in a range of from several V to 50 eV are generated from thereflection plate 17.

The secondary electron detection portion 7 is constituted by: thesecondary electron detector 20 disposed in the inside of the evacuatedinspection chamber 2; and a preamplifier 21, an AD converter 22, a lightconverting means 23, a transmission means 24, an electric convertingmeans 25, a high-voltage electric source 26, a preamplifier driveelectric source 27, an AD converter drive electric source 28, and areverse bias electric source 29 which are disposed in the outside of theinspection chamber 2. As described above, the secondary electrondetector 20 in the secondary electron detection portion 7 is disposedabove the objective lens 16 in the inspection chamber 2. The secondaryelectron detector 20, the preamplifier 21, the AD converter 22, thelight converting means 23, the preamplifier drive electric source 27 andthe AD converter drive electric source 28 are floated in a positivepotential by the high-voltage electric source 26. The second secondaryelectrons 52 generated by collision with the reflection plate 17 are ledto the detector 20 by this suction electric field. The secondaryelectron detector 20 is configured so that the second secondaryelectrons 52 generated when the secondary electrons 51 generated in aperiod of irradiation of the electron beam 19 onto theinspection-subject substrate 9 and then accelerated collide with thereflection plate 17 are detected in synchronism with the scanning timingof the electron beam 19. The output signal of the secondary electrondetector 20 is amplified by the preamplifier 21 disposed in the outsideof the inspection chamber 2 and is converted into digital data by the ADconverter 22. The AD converter 22 is configured so that the analogsignal detected by the semiconductor detector 20 is converted into adigital signal so as to be transmitted to the image processing portion 5immediately after the analog signal is amplified by the preamplifier 21.Because the detected analog signal is transmitted after digitizedimmediately after the detection thereof, a high-speed and high-SN-ratiosignal can be obtained in comparison with the conventional signal.

The inspection-subject substrate 9 is mounted on the X-Y stages 31 and32, so that there can be selected a method of two-dimensionally scanningthe electron beam 19 while keeping the X-Y stages 31 and 32 stationaryat the time of execution of inspection or a method of linearly scanningthe electron beam 19 in the X direction while continuously moving theX-Y stages 31 and 32 at a constant speed in the Y direction at the timeof execution of inspection.

The former method in which inspection is performed while the stages arekept stationary is effective for inspection of a specific, relativelynarrow region. The latter method in which inspection is performed whilethe stages are continuously moved at a constant speed is effective forinspection of a relatively wide region. Incidentally, when the electronbeam 19 is required to be blanked, the electron beam 19 can becontrolled to be deflected by the blanking deflector 13 so that theelectron beam does not pass through the aperture 14.

In this embodiment, a measuring device using laser interference was usedas the position monitoring measuring device 34. Configuration is made sothat the position of the X stage 31 and the position of the Y stage 32can be real-time monitored and transferred to the control portion 6.Configuration is made so that also data such as rotational speeds ofmotors for the X stage 31, Y stage 32 and rotation stage 33, and so on,are transferred from respective drivers to the control portion 6.Accordingly, the control portion 6 can accurately grasp the region andposition of irradiation of the electron beam 19 on the basis of thesedata and, if necessary, the positional displacement in the position ofirradiation of the electron beam 19 can be corrected in real-time by theposition correct control circuit 43. Further, the region subjected toelectron beam irradiation can be stored for every inspection-subjectsubstrate.

An optical measuring device using a measuring method other than theelectron beam method, for example, a laser interference measuring deviceor a reflected light type measuring device for measuring a change inaccordance with the position of reflected light is configured to be usedas the optical height measuring device 35 so that the height of theinspection-subject substrate 9 mounted on the X-Y stages 31 and 32 isreal-time measured. In this embodiment, there is used a method in whichlong and narrow white luminescence which has passed through a slit isirradiated onto the inspection-subject substrate 9 through a transparentwindow so that the position of reflected light is detected by theposition detection sensor and, accordingly, the quantity of change ofthe height is calculated in accordance with the change of the position.The focal length of the objective lens 16 for converging the electronbeam 19 is configured to be dynamically corrected on the basis of thedata measured by this optical height measuring device 35 so that theelectron beam 19 always focused on an inhibit area can be irradiated.Further, the warp or height distortion of the inspection-subjectsubstrate 9 can be also configured to be measured before electronic beamirradiation, so that a condition for correcting the objective lens 16 isset for every detection region in accordance with the data.

The image processing portion 5 is constituted by a first image storageportion 46, a second image storage portion 47, an arithmetic operationportion 48, a defect judgment portion 49 and a monitor 50. After asignal of an image of the inspection-subject substrate 9 detected by thesecondary electron detector 20 is amplified by the preamplifier 21 anddigitized by the AD converter 22, the signal is converted into a lightsignal by the light converter 23. After the light signal is transmittedthrough an optical fiber 24 and converted into an electric signal againby the electric converter 25, the electric signal is stored in the firstimage storage portion 46 or the second storage portion 47. Thearithmetic operation portion 48 carries out various kinds of imageprocessing for position alignment of the image signal in one storageportion with an image signal stored in the other storage portion,standardization of the signal level and removal of a noise signal tothereby perform an arithmetic operation for comparing the two imagesignals. The defect judgment portion 49 compares the absolute value ofthe differential image signal obtained by the comparison arithmeticoperation in the arithmetic operation portion 48 with a predeterminedthreshold so that, when the level of the differential image signal islarger than the predetermined threshold, the defect judgment portion 49judges the pixel as a candidate for a defect and displays the positionof the pixel and the number of defects on the monitor 50, etc.

Although the overall configuration of the circuit pattern inspectionapparatus 1 has been described above, the configuration and operation ofthe means for detecting the secondary electrons 51 will be describedbelow more in detail. When the primary electron beam 19 is incident to asolid body, energy is lost as electrons in the shell are excited at eachdepth while the primary electron beam 19 enters into the inside of thesolid body. Further, at the same time, there arises a phenomenon, asbeing expected, in which reflected electrons of the primary electronbeam scattered backward also go toward a surface of the solid body whileelectrons in the solid body are excited. After these plurality ofprocesses, electrons in the shell cross a surface barrier out of thesurface of the sold body and go into a vacuum in the form of secondaryelectrons with energy in a range of from several V to 50 eV. The smallerthe angle between the primary electron beam and the surface of the solidbody, the smaller the ratio of the penetration distance of the primaryelectron beam to the distance from the position to the surface of thesolid body, so that secondary electrons are apt to be emitted from thesurface. Accordingly, the generation of secondary electrons depends onthe angle between the primary electron beam and the surface of the solidbody, so that the quantity of generated secondary electrons becomesinformation expressing the surface roughness and material of the sample.

FIG. 2 shows a main configuration view of the electronic optical system3 and secondary electron detection portion 7 for detecting secondaryelectrons 51. When a primary electron beam 19 is irradiated onto asample substrate 9, secondary electrons 51 are generated in a surface ofthe sample substrate 9. The secondary electrons 51 are accelerated by anegative high voltage applied to the sample substrate 9. In thisembodiment, the negative voltage applied to the sample substrate 9 wasset to 3.5 keV. While accelerated, the secondary electrons 51 areconverged by the objective lens 16 and deflected by the ExB deflector 18to collide with the reflection plate 17. The reflection plate 17 isunited with a shield pipe for preventing the influence of the voltageapplied to the detector, or the like, on the primary electron beam sothat the reflection plate 17 is shaped like a cone tapered at 30degrees. The material therefore was CuBeO so that a secondary electronmultiplying effect was given as a configuration for emitting secondaryelectrons about five times as large as the number of irradiatedelectrons on average. By the collision of the accelerated secondaryelectrons 51, second secondary electrons 52 having energy in a range offrom several V to 50 eV are generated from the reflection plate 17. Thesecond secondary electrons 52 are sucked to the front surface of thesecondary electron detector 20 by the suction electric field generatedby the secondary electron detector 20 and a suction electrode 53attached to the secondary electron detector 20. In this embodiment, acondition in which the voltage and magnetic field applied to the ExBdeflector 18 and the distance between electrodes were 35 V, 1.0 10-6 T(Tesla) and 10 mm respectively was set in the case where the negativehigh voltage applied to the sample substrate 9 was 3.5 keV becausesecondary electrons 51 generated from the surface of the samplesubstrate 9 were designed so as to be deflected by about 5 degreestoward the secondary electron detector 20 by the ExB deflector 18. Theelectromagnetic field can be set so as to be changeable correspondinglyto the negative high voltage applied to the sample substrate 9.According to the aforementioned configuration and condition, 95% or moreof secondary electrons 51 generated from the surface of the samplesubstrate 9 could be made to pass through the ExB deflector 18 by thedeflection at a small angle up to about 5 degrees, the acceleration bythe −3.5 keV voltage applied to the sample substrate 9 and theconvergence based on the objective lens, so that 95% of the secondaryelectrons 51 were multiplied to a quantity of about 5-fold by thereflection plate 17 to thereby make second secondary electrons 52generated.

In this embodiment, a PIN type semiconductor detector was used as thesecondary electron detector 20. Because the PIN type semiconductordetector had higher responsibility than that of a general PN typesemiconductor detector, a high-frequency secondary electron signal witha sampling frequency not larger than 100 MHz could be detected when areverse bias voltage was applied by a reverse bias voltage electricsource. The PIN type semiconductor detector 20 and the preamplifier 21,AD converter 22 and light converting means 23 which form a detectioncircuit were floated at 6 keV and the suction electrode 53 was set to be0 V. Incidentally, the effective size of the PIN type semiconductordetector 20 is 4 mm. The second secondary electrons 52 generated fromthe reflection plate 17 are sucked by the PIN type semiconductordetector 20 on the basis of the suction electric field so that thesecond secondary electrons 52 in a high energy state enter into the PINtype semiconductor detector 20. After a predetermined amount of energyis lost by a surface layer, electron-hole pairs are generated to form anelectric current to thereby convert the electrons 52 into an electricsignal. Because the signal detection sensitivity of the PIN typesemiconductor detector 20 used in this embodiment is very high, theincident second secondary electrons 52 accelerated to 6 keV by thesuction electric field form an electric signal amplified to about 1000times, if the energy loss in the surface layer is taken intoconsideration. This electric signal is further amplified by thepreamplifier 21 and the amplified signal (analog signal) is convertedinto a digital signal by the AD converter 22. In this embodiment, a12-bit converter with a clock frequency of 100 MHz was used as the ADconverter 22. Further, a light converting means 23, a transmission means24 and an electric converting means 25 were provided for every bit sothat the output of the AD converter 22 was parallelly transmitted.According to this configuration, the transmission means may be achievedif the transmission rate in each of the transmission means is equal tothe clock frequency of the AD converter 22. Incidentally, the signalconverted into the optical digital signal by the light converting means23 is transmitted to the electric converting means 25 by the lighttransmission means 24, in which the optical digital signal is convertedinto an electric signal again so that the electric signal is fed to theimage processing portion 5. The reason why the signal is transmittedafter converted into a light signal is that the constituent elements offrom the PIN type semiconductor detector 20 to the light convertingmeans 23 are floated at a positive high potential by the high-voltageelectric source 26. According to the configuration of this embodiment, ahigh potential level signal can be converted into an earth level signal.Further, in this embodiment, a light-emitting element for converting anelectric signal into a light signal is used as the light convertingmeans 23, an optical fiber cable for transmitting the light signal isused as the transmission means 24 and a light-receiving element forconverting a light signal into an electric signal is used as theelectric converting means 25. Because the optical fiber cable is formedfrom a highly electrically insulating material, a high potential levelsignal can be easily converted into an earth potential level signal.Further, because the digital signal is optically transmitted, there isno deterioration of the signal at the time of light transmission. As aresult, an image little influenced by noise can be obtained incomparison with the prior art configuration in which the analog signalis optically transmitted. By these configurations, a high-frequencysecondary electron signal having a sampling frequency of 100 MHz can bedetected with signal SN ratio not lower than 50 in the case where thecurrent of the second secondary electrons 52 incident to the PIN typesemiconductor detector 20 is 100 nA.

Further, in the above embodiment, although a reverse bias voltage isapplied to the semiconductor detector 20 from the reverse bias voltagesource 29, another structure in which such a reverse bias voltage is notapplied may be used. Although the aforementioned embodiment has shownthe case where a PIN type semiconductor detector is used as thesemiconductor detector 20, a semiconductor detector of any other type,for example, a Schottky type semiconductor detector, an avalanche typesemiconductor detector, or the like, may be used. Further, an MCP (microchannel plate) may be also used as the detector if conditions forresponsibility, sensitivity, etc. are satisfied.

The operation in the case where a semiconductor wafer having a patternprocessed in a production process is inspected as the inspection-subjectsubstrate 9 by the aforementioned circuit pattern inspection apparatus 1will be described below. Though not shown in FIG. 1, first, thesemiconductor wafer is loaded into a sample exchange chamber by means ofcarrying the semiconductor wafer 9. In the sample exchange chamber, thesemiconductor wafer 9 is mounted on a sample holder. After thesemiconductor wafer 9 is held and fixed by the sample holder, the sampleexchange chamber is evacuated. When the degree of vacuum in the sampleexchange chamber reaches a certain value, the semiconductor wafer 9 iscarried to the inspection chamber 2 for inspection. In the inspectionchamber 2, the semiconductor wafer 9 is mounted together with the sampleholder on the sample stage 30, X-Y stages 31 and 32 and rotation stage33 and supported and fixed. The set semiconductor wafer 9 is disposed inpredetermined first coordinates under the optical microscope portion 4by the X- and Y-direction movement of the X-Y stages 31 and 32 on thebasis of predetermined inspection conditions registered in advance, sothat an optical microscopic image of the circuit pattern formed on thesemiconductor wafer 9 is observed by the monitor 50 and compared with anequivalent circuit pattern image stored in advance in the same positionfor the purpose of position rotating correction to thereby calculate aposition correction value for the first coordinates. Then, the firstcoordinates are shifted to second coordinates which are separated at apredetermined distance from the first coordinates and in which a circuitpattern equivalent to that in the first coordinates is present, so thatan optical microscopic image is observed and compared with a circuitpattern image stored for the purpose of position rotating correction inthe same manner as described above to thereby calculate a positioncorrection value for the second coordinates and the quantity ofrotational displacement from the first coordinates. The rotation stage33 is rotated by the calculated quantity of rotational displacement tothereby correct the quantity of rotation. Although this embodiment hasshown the case where the quantity of rotational displacement iscorrected by rotating the rotation stage 33, the quantity of rotationaldisplacement can be corrected also by a method of correcting thescanning deflection position of the electron beam on the basis of thecalculated quantity of rotational displacement without any rotationstage 33. In this observation of the optical microscopic image, acircuit pattern is selected so as to be able to be observed not only asan optical microscopic image but also as an electron-beam image.Further, for position correction in the future, the first coordinates,the quantity of positional displacement in the first circuit pattern onthe basis of the observation of the optical microscopic image, thesecond coordinates and the quantity of positional displacement in thesecond circuit pattern on the basis of the observation of the opticalmicroscopic image are stored and transferred to the control portion 6.

Further, the circuit pattern formed on the inspection-subjectsemiconductor wafer 9 is observed by using an optical microscopic image,so that the positions of chips in the circuit pattern on thesemiconductor wafer 9 and the distances between chips or a repetitivepitch in a repetitive pattern such as in memory cells, or the like, aremeasured in advance and the measured values are inputted into thecontrol portion 6. Further, the inspection-subject chip on theinspection-subject semiconductor wafer 9 and the inspection-subjectregion in the chip are set on the basis of the optical microscopic imageand inputted into the control portion 6 in the same manner as describedabove. Because the optical microscopic image can be observed inrelatively low magnifying power and because the subbing layer can beobserved transparently in the case where the surface of theinspection-subject semiconductor wafer 9 is coated, for example, with asilicon oxide film, or the like, the arrangement of chips and the layoutof the circuit pattern in each chip can be observed simply so that theregion to be inspected can be set easily.

When the predetermined correction work using the optical microscopeportion 4 and the preparation work for setting the region to beinspected, or the like, are completed in such a manner, thesemiconductor wafer 9 is moved under the electronic optical system 3 bythe movement of the X stage 31 and Y stage 32. When the semiconductorwafer 9 is disposed under the electronic optical system 3, the same workas the correction work carried out by the optical microscope portion 4and the same work as the work for setting the region to be inspected arecarried out by using an electron-beam image. In this occasion, theelectron-beam image is acquired by the following method. The electronbeam 19 is irradiated onto the same circuit pattern as that observed bythe optical microscope portion 4 while being two-dimensionally scannedin the X and Y directions by the scanning deflector 44 on the basis ofthe corrected coordinates stored in position alignment by using theoptical microscopic image. On the basis of the two-dimensional scanningof the electron beam, secondary electrons 51 generated from theobservation-subject region are detected by the configuration andoperation of the respective portions for detecting the secondaryelectrons to thereby acquire an electron-beam image. Because easyconfirmation of the inspection position, position alignment and positionmatching are carried out in advance by using an optical microscopicimage and because rotational correction is carried out in advance, theresolution is high in comparison with that of the optical image so thatposition alignment, position correction and rotational correction can beperformed with high magnifying power and with high accuracy.Incidentally, when the electron beam 19 is irradiated onto the sample 9,the region subjected to irradiation is electrically charged. In order toavoid the influence of the electrical charge at the time of inspection,a circuit pattern existing in the outside of the inspection region isselected in advance as the circuit pattern to be subjected to theirradiation of the electron beam 19 in the inspection preparatory workfor position/rotation correction, inspection region setting, etc. or itis designed that an equivalent circuit pattern in a chip other than thechip to be inspected can be selected automatically from the controlportion 6. By this measure, the inspection image is never influenced bythe irradiation of the electron beam 19 in the inspection preparatorywork at the time of inspection.

Then, inspection is carried out. The condition for the electron beam 19to be irradiated onto the inspection-subject semiconductor wafer 9 atthe time of inspection is obtained by the following method. First,generally, the SN ratio in an electron-beam image has correlation withthe root of the number S of irradiation electrons per unit pixel in theelectron beam irradiated onto the sample. In the case where images arecompared and inspected, the SN ratio needs be at least 10, preferablynot lower than 50 because the SN ratio in the electron-beam image needsbe a value by which the signal quantity in a normal portion and thesignal quantity in a defect portion can be detected. Because the SNratio in the electron-beam image has correlation with the root of thenumber S of irradiation electrons per unit pixel in the electron beamirradiated onto the sample as described above, at least 100 electronsper unit pixel are required for obtaining an SN ratio 10 and at least2500 electrons must be irradiated for obtaining an SN ratio 50.

Further, the main object of application of the circuit patterninspection method according to the present invention is to detect amicro defect which cannot be detected by an optical pattern inspectionmethod as described above, that is, it was necessary to recognize thedifference between images in micro pixels. In order to achieve thisobject, the pixel size in this embodiment is selected to be 0.1 μm.Accordingly, from the minimally required number of electrons per singlepixel and the aforementioned pixel size, the required quantity ofelectron beam irradiation per unit area is 0.16 μC/cm2, preferably 4μC/cm2. When this quantity of electron irradiation is to be obtainedfrom the electron-beam current (about from the order of pA to the orderof hundreds of pA) in the general SEM, 8000 seconds are required forirradiating 0.16 μC/cm2 electrons onto a region of 1 cm2, for example,at a 20 pA electron-beam current and 200000 seconds are further requiredfor irradiating 4 μC/cm2 electrons. The inspection rate required forinspection of the circuit pattern, for example, for inspection of thesemiconductor wafer is, however, not larger than 600 s/cm2, preferablynot larger than 300 s/cm2. If the inspection time is longer than thisvalue, inspection in the production of a semiconductor is of very lowpractical use. Accordingly, in order to satisfy these conditions andradiate a necessary electron beam onto the sample in a practicalinspection time, the electron-beam current need be set to be at least270 pA (1.6 μC/cm2, 600 s/cm2), preferably not smaller than 13 nA (4μC/cm2, 300 s/cm2). Therefore, the circuit pattern inspection method inthis embodiment was designed so that an electron-beam image was formedby scanning by once with a large-current electron beam not smaller than13 nA.

Further, it was cleared up from the present invention that the formationof an electron-beam image by scanning by only once with an electron beamat a large-current (not smaller than 270 nA, preferably not smaller than13 nA) not smaller than about 100 times as large as that in the generalSEM was not only necessary in terms of inspection rate but alsonecessary particularly for inspection of a circuit pattern including asubbing film or a surface pattern formed from an electrically insulatingmaterial for the following reason.

When an electron-beam image of a circuit pattern having an electricallyinsulating material is acquired by the general SEM, an electron-beamimage having a shape different from the actual shape is often obtaineddue to the influence of electric charge or the contrast is often quitedifferent in accordance with the visual field magnification. This isbecause the quantity of electron beam irradiation is concentrated into acertain place to make the electric charge of this place uneven bylocally repetitively scanning a weak electric-beam current (from theorder of pA to the order of hundreds of pA) or by locally scanning anelectric beam over the electron beam quantity required for forming animage due to the focal point or astigmatic correction at the time of thechanging of visual field magnification. As a result, the quality of anelectric-beam image of a pattern formed from an electrically insulatingmaterial becomes quietly different in accordance with the visual field,so that such an image cannot be adapted for inspection based oncomparison of electron-beam images. Accordingly, in order to make itpossible to inspect a circuit pattern having an electrically insulatingmaterial in the same manner as a circuit pattern formed from anelectrically conductive material, an electron-beam image was designed tobe formed by scanning by once with an electric beam with a large currentnot smaller than about 100 times as large as that of the general SEM.That is, in this embodiment, the quantity of electron beam irradiationonto the sample per unit area and per unit time was designed to beconstant so that an electron-beam image was acquired by scanning by oncewith an electric beam with the electron beam quantity necessary forforming sufficient image quality for comparison/inspection and with thescanning speed adapted for the practical use of the method forinspecting a semiconductor wafer, or the like. Further, it was confirmedthat the quantity of electric charge and the contrast of the image varydepending on the constituent materials and structures of various circuitpatterns constituting an electron-beam image in one visual field thatthe same image contrast was obtained in the case of the same patternformed from the same kind of material, and when an electron-beam imageof a circuit pattern having an electrically insulating material wasacquired by scanning by once with an electron beam with a large-currentnot smaller than about 100 times as large as that of the general SEM asdescribed above. Although this embodiment has shown the case wherescanning of a large-current electron beam is carried out only once,scanning may be carried out several times in a range where theaforementioned operation can be realized substantially.

FIGS. 3( a), 3(b) and 3(c) typically show secondary electron generationefficiency and the degree of electric charge in the case where anelectron beam is irradiated onto a point P of a sample. In FIG. 3( a),the vertical axis expresses the relative intensity of a primary electronbeam irradiated onto the sample and the horizontal axis expresses timeand distance. In FIG. 3( b), the vertical axis expresses the relativedegree of electric charge of the sample and the horizontal axisexpresses time. In FIG. 3( c), the vertical axis expresses the relativequantity of generated secondary electrons and the horizontal axisexpresses time. When an electron beam is irradiated onto a sample by theaforementioned inspection method according to the present invention, theelectron beam passes through the point P while scanning the point P at ahigh speed. In the time of 10 ns, a relatively intensive portion of theelectron beam passes through the point P. In this embodiment, the timeof 10 ns is equivalent to one pixel because the scanning speed of theelectron beam is set to 100 MHz per pixel. Further, in this embodiment,the time of 10 ns is equivalent to 0.1 μm because one pixel is selectedto be 0.1 μm″. When the electron beam is irradiated onto the sample atthe point P in the timing of FIG. 3( a), the sample is electricallycharged as shown in FIG. 3( b). The degree of electric charge and thedegree of electric discharge with the passage of time vary in accordancewith the material for the sample. When the sample is an electricallyinsulating material, electric charge may remain after the passage of theelectron beam so that electric discharge is not carried out unless along time is passed. As shown in FIG. 3( c), secondary electrons aregenerated after an instance when the primary electron beam is irradiatedonto the sample. The quantity of the generated secondary electronsdepends on the secondary electron generation efficiency determined bymaterial and the degree of electric charge shown in FIG. 3( b).Accordingly, for example, in the first scanning, the quantity of thesecondary electrons shown in FIG. 3( c) are generated and, in the secondscanning, the quantity of generated secondary electrons varies in thecase where the degree of electric charge in the second scanning isdifferent from the degree of electric charge in the first scanning.

Irradiation conditions having influence on the contrast of theelectron-beam image will be described below. The contrast of theelectron-beam image is formed in accordance with the quantity ofsecondary electrons generated by the electron beam irradiated onto thesample and detected. For example, the difference in the quantity ofgenerated secondary electrons caused by the difference in material formsthe difference in brightness. FIGS. 4( a) and 4(b) are graphs showingthe influence of the electron beam irradiation condition on thecontrast. FIG. 4( a) shows the case where the irradiation condition issuitable, and FIG. 4( b) shows the case where the irradiation conditionis unsuitable. Further, the vertical axis expresses the degree ofelectric charge which has a large correlation with the brightness of theimage and the horizontal axis expresses the time of electron beamirradiation. The solid line A shows the case where a photo resist isused as the sample and the broken line B shows the case where a wiringmaterial is used as the sample.

From FIG. 4( a), the fluctuation of the brightness of each material issmall in the time region C in which the irradiation time is short, thechange of the brightness by the irradiation time becomes large in thetime region D in which the irradiation time becomes relatively long, andfinally, the fluctuation of brightness by the irradiation time becomessmall again in the time region E in which the irradiation time is long.Further, from FIG. 4( b), when the irradiation condition is unsuitable,the fluctuation of brightness with respect to the irradiation time islarge even in the time region C in which the irradiation time is short,so that it is difficult to obtain a stable image. Accordingly, in orderto acquire a high-speed and stable electron-beam image, it is importantto acquire the image in the irradiation condition of FIG. 4( a).

Examples of the condition for irradiation of the electron beam onto thesample include the irradiation quantity of the electron beam per unitarea, the current value of the electron beam, the scanning speed of theelectron beam, and the irradiation energy of the electron beamirradiated onto the sample. Therefore, it is necessary to obtain optimumvalues of these parameters correspondingly to the shape and material ofthe circuit pattern. Therefore, it is necessary to freely adjust andcontrol the irradiation energy of the electron beam irradiated onto thesample. Therefore, as described above, this embodiment is configured sothat the high-voltage electric source 36 applies a negative voltage forretarding the primary electrons to the semiconductor wafer 9 which isthe sample and so that the irradiation energy of the electron beam 19can be suitably controlled by controlling this voltage. Although theaxial change of the electron beam 19 occurs and various adjustments arerequired when the acceleration voltage applied to the electron gun 10 ischanged, the same effect can be obtained in this embodiment by thismeasure without such adjustments.

The method of scanning the electron beam 19 for forming an electron-beamimage to perform inspection according to the present invention will bedescribed below. In the general SEM, an image of a certain region isformed by two-dimensionally scanning an electron beam in a state inwhich the stages are made stationary. According to this method, when awide region is to be inspected thoroughly, there are required not onlythe time for making the stages stationary and scanning the electron beamby region for acquiring an image but also the time obtained by addingthe acceleration, deceleration and position control of the stages as themoving time. Accordingly, a long time is required as the whole of theinspection time. Accordingly, in the present invention, there is used aninspection method in which an image of an inspection-subject region isacquired by scanning an electron beam at a high speed in one directionperpendicular to or crossing the direction of the movement of the stageswhile continuously moving the stages in one direction at a constantspeed. By this method, the time for acquiring one-scanning-width'selectric beam at a predetermined distance is made equal to only the timefor moving the stages by the predetermined distance.

FIG. 5( a) shows an example of the method of scanning the electron beam19 when the Y stage 32 is continuously moved in Y direction at aconstant speed by the aforementioned method. When the electron beam 19is to be scanned by the scanning deflector 44, by irradiating theelectron beam onto the semiconductor wafer 9 which is the sample, onlyin one direction expressed by the solid line and performing blanking sothat the electron beam 19 is not irradiated onto the semiconductor wafer9 in the electron beam return period expressed by the broken line, theelectron beam can be irradiated onto the semiconductor wafer 9 evenly interms of space and time. The electron beam 19 is deflected by theblanking deflector 13 so as not to pass through the aperture 14 tothereby perform blanking.

FIG. 5( b) shows, as another example of the scanning method, a method inwhich the electron beam 19 makes a reciprocating motion at a constantspeed for scanning. When the electron beam 19 is scanned from one end tothe opposite end at a constant speed, the X-Y stages 31 and 32 are fedby one pitch so that the electron beam is scanned toward the originalend in a reverse direction at a constant speed. In the case of thismethod, the return time of the electron beam can be omitted.

Incidentally, the region or position on which the electron beam isirradiated is grasped in detail by real-time transferring themeasurement data of the position monitoring measuring device 34 disposedin the X-Y stages 31 and 32, to the control portion 6. In thisembodiment, a laser interferometer is employed. Similarly, the change inheight of the region or position on which the electron beam 19 isirradiated is grasped in detail by real-time transferring themeasurement data of the optical height measuring device 35, to thecontrol portion 6. The displacement in the irradiation position of theelectron beam and the displacement in the focal position thereof arecalculated on the basis of these data, so that these positionaldisplacements are corrected automatically by the position correctcontrol circuit 43. Accordingly, a method of operating an electron beamaccurately and exactly is secured.

By the aforementioned method of scanning the electron beam 19, theelectron beam is irradiated onto the whole surface of the semiconductorwafer 9 which is the sample or onto a preliminarily set inspectionregion, so that secondary electrons 51 are generated by theaforementioned principle and secondary electrons 51 and 52 are detectedby the aforementioned method. A good-quality image can be obtained bythe configuration and operation of the respective parts. For example,not only about a 20-fold secondary electron multiplying effect can beobtained by irradiating secondary electrons onto the reflection plate 17by the aforementioned configuration and method but also the influence ofaberration on the primary electron beam can be suppressed compared withthe conventional method. Further, second secondary electrons 52 obtainedby irradiating reflected electrons generated from a surface of thesemiconductor wafer 9 onto the reflection plate 17 in the same manner asin the secondary electrons can be detected easily by adjusting theelectromagnetic field applied to the ExB deflector in the sameconfiguration. Further, secondary electrons can be detected efficientlyeven in different irradiation conditions corresponding to samples bycontrolling the electric field and magnetic field of the ExB deflector18 so as to be interlocked with the negative high voltage applied toeach sample. Further, by the method of detecting secondary electrons byusing the semiconductor detector 20, digitizing the detected imagesignal just after the detection and optically transmitting the digitalsignal, the influence of noise generated in various conversion andtransmission is reduced so that high SN image signal data can beobtained. In a process in which an electron-beam image is formed on thebasis of the detected signal, the image processing portion 5 makes thefirst or second storage portion 46 or 47 store sequentially a signaldetected in a time corresponding to a desired pixel in the electron beamirradiation position designated by the control portion 6 as a brightnessgradation value corresponding to the signal level of the detectedsignal. By relating the electron beam irradiation position to thequantity of secondary electrons related to the detection time, anelectron-beam image of the circuit pattern in the sample is formedtwo-dimensionally. In this manner, a high-accurate, high-SN-ratio andgood-quality electron-beam image can be made to be acquired. Althoughthe above description of this embodiment has been made about theinspection method and apparatus in which secondary electrons generatedfrom the sample are detected, not only the secondary electrons but alsobackward scattered electrons and reflected electrons are generated fromthe sample. These secondary charged particles as well as the secondaryelectrons can be detected as an electron-beam image signal in the samemanner as described above.

When the image signal is transferred to the image processing portion 5,the electron-beam image of the first region is stored in the firststorage portion 46. The arithmetic operation portion 48 carries outvarious kinds of image processing for position alignment of the storedimage signal with an image signal in the other storage portion,standardization of signal level and removal of a noise signal.Successively, while the electron-beam image of the second region isstored in the second storage portion 47 and the same arithmeticoperation processing as described above is applied thereto, there iscarried out an arithmetic operation based on comparison between theelectron-beam image of the second region and an image signal in one andthe same circuit pattern and one and the same position in the firstelectron-beam image. The defect judgment portion 49 compares theabsolute value of the differential image signal obtained by thecomparison and arithmetic operation in the arithmetic operation portion48 with a predetermined threshold. When the level of the differentialimage signal is larger than the predetermined threshold, the defectjudgment portion 49 judges the pixel as a candidate for a defect anddisplays the position thereof, the number of defects, etc. on themonitor 50. While the electron-beam image of the third region is thenstored in the first storage portion 46 and the same arithmetic operationis applied thereto, the electron-beam image is compared with theelectron-beam image of the second region previously stored in the secondstorage portion 47 to thereby judge a defect. Thereafter, this operationis repeated so that image processing is executed upon all the detectionregions.

By the aforementioned inspection method, a micro defect generated on amicro circuit pattern can be detected in a practically effectiveinspection time by acquiring a high-accurate good-quality electron-beamimage and performing comparison and inspection. Further, a patternformed from a silicon oxide film or a resist film and foreign matter ordefects in these materials can be detected by acquiring an image by useof an electron beam though inspection cannot be performed by the opticalpattern inspection method because light is transmitted. Further,inspection can be performed stably even in the case where the materialforming the circuit pattern is an electrically insulating material.

Embodiment 2

In this embodiment, there will be described an applied example in whicha semiconductor wafer is inspected by using the circuit patterninspection apparatus 1 and method according to the present invention.FIG. 6 shows a process for producing a semiconductor device. As shown inFIG. 6, a large number of pattern forming processes are repeated in thesemiconductor device. The pattern forming process is roughly constitutedby the steps of deposition, application of a light-sensitive resist,exposure, development, etching, resist removal and cleaning. If theproduction condition for processing is not optimized in each step, acircuit pattern of the semiconductor device formed on the substrate isnot formed normally. FIGS. 7( a) and 7(b) schematically show a circuitpattern formed on a semiconductor wafer in a production process. FIG. 7(a) shows a circuit pattern processed normally, and FIG. 7( b) shows acircuit pattern in which a failure in processing occurs. When, forexample, abnormality occurs in the step of deposition in FIG. 6,particles are generated and deposited on a surface of the semiconductorwafer so that an isolated defect, or the like, is formed as shown inFIG. 7( b). Further, if the condition for the focal point, exposuretime, etc. of an exposure device for performing exposure at the time ofexposure is not optimized, a region of the resist in which the quantityor intensity of light to be irradiated is too large or a region of theresist in which the quantity or intensity of light to be irradiated istoo small is generated to thereby bring short-circuiting, breaking andpattern tapering as shown in FIG. 7( b). When there is some defect in amask/reticle at the time of exposure, the same abnormality in patternshape occurs in one and the same region correspondingly to a shot whichis the unit of exposure. Further, short-circuiting or a projection, anisolated defect, a failure in opening, etc. are generated because of athin film or particles generated in the case where the quantity ofetching is not optimized and in the middle of etching. At the time ofcleaning, micro particles are generated by re-deposition of stain of acleaning layer and of film and particles peeled so that irregularity inthickness of oxide film is apt to occur in its surface correspondinglyto the dewatering condition at the time of drying.

Accordingly, by applying the circuit pattern inspection method andapparatus 1 of Embodiment 1 to a semiconductor device producing process,the occurrence of abnormality can be detected with a high accuracy in anearly stage so that a measure counter to abnormality can be given to theprocess and that the processing condition can be optimized to preventthe occurrence of these failures. When, for example, a defect or breakin a photo resist pattern is detected by execution of a circuit patterninspection process after a development process, the situation in whichthe exposure condition and focal point condition for the exposure devicein the exposure process are not optimized is inferred, and theseconditions are improved immediately by adjustment, or the like, of thefocal point condition or the quantity of exposure. Further, by judgingfrom a defect distribution whether these defects occur in common torespective shots or not, defects in the photo mask reticle used inpattern forming are inferred so that inspection or exchange of the photomask/reticle is carried out quickly. The same thing is applied to otherprocesses, and various kinds of defects' are detected by applying thecircuit pattern inspection method and apparatus according to the presentinvention and carrying out the inspection process so that the cause ofabnormality in each producing process is inferred from the content ofthe detected defect.

Because the change of various producing conditions and the occurrence ofabnormality can be detected in a real inspection time by carrying outthe circuit pattern inspection method and apparatus 1 in thesemiconductor device producing process in line, the occurrence of alarge quantity of failures can be prevented. Further, the efficiencypercentage in the whole semiconductor device can be predicted on thebasis of the degree of the defect, the frequency in occurrence of thedefect, and so on, detected by application of the circuit patterninspection method and apparatus, so that efficiency in production of thesemiconductor device can be improved.

Embodiment 3

The third embodiment of the present invention as to the configuration ofthe inspection apparatus is configured in the same manner as in thefirst embodiment except that an objective lens 16 in the electronicoptical system 3 is disposed above the secondary electron detector 20 asshown in FIG. 8. FIG. 8 shows an enlarged partial view of the inside ofthe inspection chamber 2 in the circuit pattern inspection apparatus.The operation based on the configuration of the third embodiment will bedescribed below. An electron beam 19 is irradiated onto aninspection-subject substrate 9 in the same method as in the firstembodiment. A negative high voltage is applied to the inspection-subjectsubstrate 9 in the same manner as in the first embodiment. In thisembodiment, the negative voltage for retarding primary electrons appliedto the inspection-subject substrate 9 is selected to be −3.5 keV. Byelectron beam irradiation, secondary electrons 51 are generated from asurface of the sample substrate 9 by the aforementioned operation.Because the secondary electrons 51 generated from the surface of thesample substrate 9 are accelerated to 3.5 keV rapidly by the negativevoltage applied to the sample substrate 9, the direction of thesecondary electrons 51 generated from the surface of the substrate 9 isarranged in line. Because the spread of the accelerated secondaryelectrons 51 at the time of collision with the reflection plate 17 isnot larger than the order of mm, detecting efficiency is not loweredeven if the secondary electrons 51 are not converged by the objectivelens 16. Accordingly, because second secondary electrons 52 generated bycollision of the accelerated secondary electrons 51 with the reflectionplate 17 can be detected as a signal with high efficiency even in theconfiguration of this embodiment in which the objective lens 16 isdisposed in a position for converging only the primary electron beam 19,a good-quality electron-beam image can be acquired. According to thisembodiment, the focal length of the objective lens 16 is elongatedcompared with the first embodiment and, as a result, resolution andaccuracy can be maintained even in the case where the primary electronbeam 19 is deflected widely compared with the first embodiment. Thisembodiment as to the other configuration and operation is the same asthe first embodiment, and the description thereof will be omitted.

Embodiment 4

The fourth embodiment is configured in the same manner as in the firstembodiment except that the reflection plate 17 is curved. FIG. 9 showsan enlarged portion view showing the configuration of the reflectionplate portion. In this embodiment, because the reflection plate 17united with the shield pipe is curved, the angle of generation of secondsecondary electrons 52 is changed correspondingly to the position of thereflection plate 17 when secondary electrons 51 generated from a surfaceof the sample substrate 9 by irradiating an electron beam 19 onto thesample substrate 9 are accelerated by the negative high voltage appliedto the sample substrate 9, deflected by the ExB deflector 18 andirradiated onto the reflection plate 17. As a result, second secondaryelectrons 52 generated by collision with any region of the reflectionplate 17 are made easy to be grasped by the semiconductor detector 20.Accordingly, because not only the range for selecting the angle ofdeflection of secondary electrons 51 is widened when the acceleratedsecondary electrons 51 are deflected by the ExB deflector 18 but also asignal can be detected with high efficiency even in the case where theangle of generation of the secondary electrons 51 generated from thesurface of the sample substrate 9 is widened, a good-qualityelectron-beam image can be obtained. This embodiment as to the otherconfiguration and operation is the same as the first embodiment, and thedescription thereof will be omitted.

Embodiment 5

The fifth embodiment will be described below as to the configuration ofthe method and apparatus in which the inspection-subject substrate iselectrically charged by irradiating a second charged particle beam ontothe sample substrate so that inspection is performed after the potentialof a member forming a circuit pattern in the inspection-subjectsubstrate becomes stable.

FIG. 10 shows the configuration of the circuit pattern inspectionapparatus 1 according to the fifth embodiment. The circuit patterninspection apparatus 1 comprises an inspection chamber 2 evacuated, afirst sub chamber (not shown in this embodiment) for carrying a sampleinto the inspection chamber 2, a second sub chamber 100 for irradiatinga second charged particle beam, a control portion 6, and an imageprocessing portion 5. The first sub chamber (not shown) and the secondsub chamber 100 are configured so as to be able to be evacuatedindependent of the inspection chamber 2. Further, the second sub chamber100 has an electron gun 101, a lens 102, and a large angle deflectioncoil 103. The inside of the inspection chamber 2 is roughly constitutedby an electronic optical system 3, a secondary electron detectionportion 7, a sample chamber 8, and an optical microscope (not shown).The electronic optical system 3 has an electron gun 10, an electronextraction electrode 11, a condenser lens 12, a blanking deflector 13, ascanning deflector 15, an aperture 14, an objective lens 16, areflection plate 17, and an ExB deflector 18. In the secondary electrondetection portion 7, a secondary electron detector 20 is disposed abovethe objective lens 16 in the inspection chamber 2. The output signal ofthe secondary electron detector 20 is amplified by a preamplifier 21disposed in the outside of the inspection chamber 2 and converted intodigital data by an AD converter 22. The sample chamber 8 has a samplestage 30, X-Y stages 31 and 32, a rotation stage 33, a positionmonitoring measuring device 34, and an inspection-subject substrateheight measuring device 35. The optical microscope (not shown) isdisposed near the electronic optical system 3 in the inspection chamber2 but at a distance where the microscope and the optical system are notinfluenced by each other. The distance between the electronic opticalsystem 3 and the optical microscope is known. An electron-beam image oroptical image taken in is displayed on a monitor 50. Instructions andconditions for operating respective portions of the apparatus areinputted/outputted through the control portion 6. Conditions such as theaccelerated voltage at the time of generation of an electron beam, theelectron-beam deflection width, the deflection speed, the signal fetchtiming of the secondary electron detector, the moving speed of thesample stage, etc. are inputted into the control portion 6 in advance soas to be able to be set freely or selectively in accordance with thepurpose. Using a position correct control circuit 43, the controlportion 6 monitors positional or height displacement on the basis ofsignals of the position monitoring measuring device 34 and theinspection-subject substrate height measuring device 35, generatescorrect signals from the results of monitoring and feeds the correctsignals to the objective lens electric source 45 and the scanningdeflector 44 so that the electron beam 19 is always irradiated onto ancorrect position. The image processing portion 5 has image storageportions 46 and 47, an arithmetic operation portion 48, and a defectjudgment portion 49. An electron-beam image signal detected by thesecondary electron detection portion 7 is stored in the image storageportion. After various arithmetic operations are carried out, the imageis compared with another adjacent electron-beam image to extract only adefect portion.

The second sub chamber 100 will be described below in detail. Theelectron gun 101 and the lens 102 disposed in the sub chamber 100 aredisposed near the electronic optical system 3 in the inspection chamber2 but at a distance therefrom so that the gun or the lens and theoptical system are not influenced by each other. By a substrate carryingmeans, the inspection-subject substrate 9 is loaded into the first subchamber (not shown) which is a sample exchange chamber. In the first subchamber, the inspection-subject substrate is put in a sample holder andheld and fixed. When the first sub chamber is then evacuated so that thedegree of vacuum in the first sub chamber, that is, the sample exchangechamber, reaches a certain value, the inspection-subject substrate iscarried to the second sub chamber 100 together with the sample holder.The second sub chamber 100 is evacuated in advance. In the second subchamber 100, a sub irradiation electron beam 104 from the electron gun101 is irradiated onto the inspection-subject substrate 9. Alarge-current type gun having a large light source is suitable as theelectron gun 101. In this embodiment, there was used an oxide cathode inwhich low work function oxide used in a CRT monitor was heated by aheater to thereby emit thermoelectrons. The electron lens 102 isdisposed to limit the irradiation region of the sub irradiation electronbeam 104 from the electron gun 101 to a certain degree so that thediameter of the sub irradiation electron beam 104 on theinspection-subject substrate 9 can be narrowed from the order of cm tothe order of mm. The large angle deflector 103 is of the type capable ofbeing deflected in a very wide angle range as used in a CRT monitor suchas a television set, or the like. For example, even in the case wherethe inspection-subject substrate is a semiconductor wafer having a sizeof 8 inches or not smaller than 12 inches, the sub irradiation electronbeam 104 can be scanned on the inspection-subject substrate 9 all overthe sample by the deflector 103. In this occasion, the current and thenumber of times for scanning and the scanning speed in the subirradiation electron beam 104 are selected to be constant so that thequantity of irradiation of the electron beam is made uniform in terms oftime and space. Further, the irradiation energy of the sub irradiationelectron beam 104 in the sub chamber 100 is selected to be equal to theirradiation energy of the electron beam 19 irradiated in the inspectionelectronic optical system 3 in the inspection chamber 2. While theelectron beam 104 is irradiated in the second sub chamber 100 asdescribed above, another inspection-subject substrate 9′ is set in theinspection chamber 2 adjacent to the second sub chamber 100 so thatinspection is executed by the electron beam 19 from the electron gun 10.That is, the inspection chamber 2 and the second sub chamber 100 areconfigured so that the operations thereof can progress independent ofeach other. Because the irradiation of the sub irradiation electron beam104 in the second sub chamber 100 can be processed in a sufficientlyshorter time than the time required for inspection, the time requiredfor inspection as a whole is little increased even in the case where theinspection-subject substrate 9 is pre-treated in the second sub chamber100.

The inspection-subject substrate 9 is electrically charged byirradiating the sub electron beam 104 onto the inspection-subjectsubstrate 9. As described above in the first embodiment, theelectrically charged state of the inspection-subject substrate 9 ischanged correspondingly to the time and energy of irradiation of theelectron beam, so that the contrast of the resulting image is changed.FIGS. 11( a) and 11(b) show the influence of the electron beamirradiation time on the contrast. FIG. 11( a) shows the case where aphoto resist (solid line A) and a wiring material (broken line B) areused as the sample shown in FIG. 4( a). FIG. 11( b) shows the case wherea photo resist (solid line A) and a silicon oxide film (broken line C)are used as the sample. The change of brightness in each material issmall in the region F in which the irradiation time is small. The changeof brightness with the passage of time is large so as to be unstable inthe time region G in which the irradiation time is relatively large. Thechange of brightness with the passage of time becomes small again in thetime region H in which the irradiation time is large. In a combinationof the two samples in FIG. 11( a), the difference in brightness betweenthe two materials, that is, contrast D in the time region F becomeslarge. In a combination in FIG. 11( b), however, contrast. E′ in thetime region H becomes large. Because the inspection of the circuitpattern is based on comparison, the larger in contrast between thesub-layer material and the surface material forming the pattern isuseful for detection of a defect. It is to be understood that theirradiation time or the electrically charged state for obtaining anelectron beam stable in brightness and high in contrast variescorrespondingly to the combination of materials for forming the circuitpattern. Although the first embodiment has shown the case whereinspection is performed in the irradiation time zone F in FIG. 11( a),the inspection-subject substrate 9 can be set in the electricallycharged state in the time region H in advance before inspection when theinspection-subject substrate 9 is electrically evenly charged by theirradiation of the sub irradiation electron beam 104 in this embodiment.Thereafter, an electron-beam image is acquired by the irradiation of theelectron beam 19 in the inspection chamber 2 so that inspection of thecircuit pattern is performed.

When the irradiation of the sub irradiation electron beam 104 in thesecond sub chamber 100 is completed, the inspection-subject substrate 9together with the sample holder is put on the sample stage 30 forinspection, X-Y stages 31 and 32 and rotation stage 33 and held andfixed. This embodiment as to the inspection method after that is thesame as the first embodiment, and the description thereof will beomitted. By performing inspection according to this embodiment, theelectron-beam image in the optimum condition for carrying out comparisoninspection, that is, brightness was made stable for every combination ofmaterials, so that an electron-beam image large in the contrast of themember forming the circuit pattern could be obtained. Further, because ahigh-SN good-quality image could be obtained at a high speed by theinspection method described above in the first embodiment, a microdefect could be detected with a high accuracy and a high sensitivitywithout false detection of any non-defect portion even in the inspectionusing an electrically insulating material, or the like.

Embodiment 6

In the sixth embodiment, the configuration and method for irradiatingthe sub irradiation electron beam 104 onto the inspection-subjectsubstrate 9 without provision of the sub irradiation second sub chamber100 described above in the fifth embodiment will be described. The basicconfiguration of this embodiment is the same as that of the firstembodiment except that a second electron source is added to theelectronic optical system 3. FIG. 12 is a main configuration view of theinspection chamber 2 in the inspection apparatus 1. As for the detailsof the control portion 6, the image processing portion 5, the detectionsystem and others, reference is to be made to the first embodiment.There is a configuration in which an electron beam emitted from thesecond electron gun 110 is introduced in between the objective lens 16and the condenser lens 12 in the electronic optical system 3. Thepotential in the second electron gun 110 is generally selected to be thesame negative potential as that in the image-forming electron gun.Further, the electron beam 104 emitted from the second electron gun 110is converged by a second condenser lens 111 and deflected toward theinspection-subject substrate 9 put on the sample stage by a deflector112 for joining the electron beam to the optical axis of the electronicoptical system. FIG. 13 shows the principle of an electromagnet typedeflector as an example of the deflector 112. A coil is wound axially ona cylindrical ferromagnetic body so that a current flows in the coil.Accordingly, a circumferential-direction magnetic field is present inthe ferromagnetic body. A small hole is opened in a side wall of thecylindrical ferromagnetic body and disposed so that the second electronbeam enters into the small hole. Because the magnetic field in theferromagnetic body is leaked out to a space in the small hole, thesecond electron beam passing through the space is deflected so as to beintroduced into the optical axis of the electronic optical system. Then,the electron beam advances substantially on the same optical axis as theimage-forming electron beam and is irradiated onto theinspection-subject substrate. Because the image-forming condition in thesecond electron beam is, however, different from that in theimage-forming electron beam, the second electron beam is not focused onthe inspection-subject substrate.

Incidentally, a method in which the sub irradiation electron beam 104and the image-forming electron beam 19 advancing substantially on thesame optical axis are irradiated simultaneously and a inspection methodin which the two electron beams are irradiated while the timing isshifted are thought of. In the case of simultaneous irradiation, acorrect electron-beam image cannot be obtained generally because thesecondary electrons generated by irradiation of the image-formingelectron beam 19 and the secondary electrons generated by the subirradiation electron beam 104 cannot be detected so as to bediscriminated. In the case where the diameter of the sub irradiationelectron beam 14 is sufficiently larger than the diameter of theimage-forming electron beam 19 as shown in FIGS. 14( a) and 14(b),however, the level of the secondary electrons generated by the subirradiation electron beam 14 becomes substantially a background signallevel so that the electron-beam image to be formed is substantiallyformed from the image signal based on the irradiation of theimage-forming electron beam 19. Therefore, the condenser lens 111 of thesecond electron gun 110 is adjusted so that the sub irradiation electronbeam 104 is not focused on the surface of the inspection-subjectsubstrate 9 but has a size not smaller than 10 μm. FIGS. 14( a) and14(b) show the sectional beam profiles of the second electron beam 104and the image-forming electron beam 19 irradiated onto theinspection-subject substrate 9. Although FIG. 14( a) shows the casewhere the image-forming electron beam 19 is located in the center of theelectron beam from the second electron gun 110, the centers of thesecond electron beam and the image-forming electron beam need not bealways coincident with each other as shown in FIG. 14( b). Preferably,the image-forming electron beam 19 is designed to be located with in therange of the diameter of the electron beam from the second electron gun110. This is because to prevent such a fact that if the two electronbeams are at a large distance from each other, there arises thenecessity of widening the operating range of the scanning deflector inorder to scan the two electron beams to an inhibit area so that as aresult, the inspection time is prolonged.

Further, in the case where the image-forming electron beam 19 and theelectron beam 104 from the second electron gun 110 are irradiated ontothe inspection-subject substrate while the timing of irradiation isshifted, the sub irradiation electron beam 104 is designed to beirradiated in a period in which the scanning of the image-formingelectron beam 19 is returned. Because the image-forming electron beam 19is raster-scanned linearly or two-dimensionally as occasion demands sothat the image signal is not acquired in a period in which, for example,the electron beam is returned to the left of the image acquirementregion after linear scanning of the electron beam from the left to theright, secondary electrons generated by irradiating the sub irradiationelectron beam 104 in the return period have no influence on the image.

Also by the aforementioned method for irradiating an electron beam fromthe second electron gun 110, a good-contrast stable image can beobtained because the image is an image after the potential based onelectric charge is stabilized as described above in the fifthembodiment.

Embodiment 7

In the seventh embodiment, there will be described the configuration ofthe method and apparatus in which the second electron source for the subirradiation electron beam 104 described in the sixth embodiment isprovided in the peripheral portion of the aperture though which theimage-forming electron beam is irradiated. FIGS. 15( a) and 15(b) showthe portion of the electronic optical system in the seventh embodiment.This embodiment as to other portions is the same as in the fourth andsixth embodiments. As shown in FIG. 15( a), a front end of the objectivelens 16 is shaped like a truncated cone so that an electron gun 120 forthe sub irradiation electron beam 104 is disposed in a space facing theinspection-subject substrate 9. A gun having a large light source toobtain a large current is suitable as the electron gun 120. In thisembodiment, there was used an oxide cathode in which low work functionoxide used in a CRT monitor was heated by a heater to thereby emitthermoelectrons. The energy of irradiation of the electron beam from thesecond electron gun 120 onto the inspection-subject substrate 9 isselected to the same as that of the image-forming electron beam 19.Further, the electron gun 120 for the sub irradiation electron beam 104is constituted by two or four electron guns which are disposed so as tobe two-fold or four-fold symmetric with respect to the center on theaxis in which the stages are continuously moved at the time of theformation of the image, the electron guns being designed so as tooperate independently of each other. The arrangement of the electronguns 120 is shown in FIG. 15( b) which is a view when the lower surfaceof the objective lens 16 is seen from the side of the inspection-subjectsubstrate 9. The plurality of electron guns 120 operate so that subirradiation electron beams 104 are irradiated onto places just beforescanning of the image-forming electron beam is performed correspondinglyto the direction of the movement of the stage. When, for example, thestage is moved from left to right as shown in FIG. 15( a), the secondelectron gun 120 in the left of FIG. 15( b) operates.

Further, this embodiment can be configured by the following method sothat secondary electrons generated by the sub electron irradiation 104have no bad influence on the electron-beam image even in the case wherethe irradiation of the sub electron beam 104 and the image-formingelectron beam 19 are performed simultaneously. FIG. 16 shows a typicalview of this method. Secondary electrons 51 generated from theinspection-subject substrate 9 moves up in the objective lens 16 on thebasis of the acceleration electric field described above in detail inthe first embodiment. In this occasion, the secondary electrons areinfluenced by the magnetic field in the objective lens so as to befocused. The horizontal position of this focal point variescorrespondingly to the place of generation of the secondary electrons.For example, secondary electrons generated from a point A in the surfaceof the inspection-subject substrate are focused at A′, and secondaryelectrons generated from a point B are focused at B′. Accordingly, byproviding an aperture 121 in the focal point position of the secondelectrons and arranging the secondary electron detector 20 above theaperture, secondary electrons generated from the vicinity of the centerof the optical axis, that is, from the place onto which theimage-forming electron beam 19 is irradiated can be detectedselectively. Because the position of irradiation of the sub electronbeam 104 is at a distance of the order of hundreds of μm from theposition of irradiation of the image-forming electron beam 19, secondaryelectrons generated by the sub irradiation electron beam 104 are blockedby the aperture so as not to be detected. Also in this embodiment, thesame good-contrast image as in the fifth or sixth embodiment could beacquired after the sample was electrically charged in advance and thepotential was stabilized.

Embodiment 8

For example, in a semiconductor device producing process, theinspection-subject substrate may have been already subjected to electronbeam irradiation not only by the circuit pattern inspection apparatusaccording to the present invention but also by inspection, observation,or the like, using the SEM. In such a case, a local portion of a surfaceof the inspection-subject substrate may have been already electricallycharged before execution of the circuit pattern inspection, so that itis difficult that the locally electrically charged region iselectrically evenly charged so as to be equal to other regions by theinspection method according to the aforementioned embodiments.Accordingly, the locally electrically charged region may be unable to beinspected because a specific contrast electron-beam image is formed fromthe region. To avoid this situation, the electric charging of thesurface is preferably neutralized before circuit pattern inspection iscarried out according to the aforementioned respective embodiments.

In this embodiment, a second sub chamber 130 is added to theconfiguration of the circuit pattern inspection apparatus 1 described inthe first embodiment so that plasma is irradiated onto theinspection-subject substrate in the second sub chamber 130 beforeinspection. FIG. 17 shows the partial configuration of the inspectionchamber 2 and the second sub chamber 130 in this embodiment.

A gas introduction inlet 131 and electrodes 132 for applying an electricfield for ionizing an introduced gas are disposed in the second subchamber 130. A high-frequency electric source 131 is connected to theelectrodes 132. After the first sub chamber (not shown) is evacuated,the inspection-subject substrate 9 put in the sample holder in the firstsub chamber is carried to the second sub chamber 130 already evacuated.Then, rare gases such as Ar, etc., and air having a pressure not largerthan the order of Pa are introduced into the second sub chamber 130, anda high-frequency voltage is applied between the electrodes 132 so thatthese gases are ionized to form plasma 133. The inspection-subjectsubstrate 9 is left in the plasma 133 for a predetermined period, sothat the electrically charged portion is neutralized during the period.After this pre-treatment is carried out, the inspection-subjectsubstrate 9 is carried into the inspection chamber 2 for performinginspection. The inspection method has been described above in detail inthe first embodiment, and the description thereof will be omitted.Because the local electric charging of the inspection-subject substrate9 is neutralized by the pre-treatment described in this embodiment justbefore inspection, the surface of the inspection-subject substrate 9 iselectrically evenly charged when an electron-beam image is acquired byirradiating an electron beam at the time of inspection. Accordingly,because the electron-beam image used for comparison inspection becomesuniform in contrast, high-accurate and stable inspection can beperformed. In a period of the irradiation of the plasma 113 in the subchamber 130 described in this embodiment, another inspection-subjectsubstrate 9′ is set in the inspection chamber adjacent to the subchamber 130, and inspection is performed. Because the time required forthe pre-treatment using plasma irradiation is sufficiently shorter thanthe time required for the inspection, the inspection time as a whole islittle increased by performing the pre-treatment.

Although the typical configuration of the apparatus and the circuitpattern inspection method according to the present invention have beendescribed above by way of embodiments as to the method in which anelectron-beam image is acquired at a high speed by electron beamirradiation so as to be used for comparison inspection, the method inwhich inspection is performed after the potential of theinspection-subject substrate is stabilized by irradiation of a secondcharged particle beam, the method in which secondary electrons generatedfrom the inspection-subject substrate are detected efficiently to obtaina good-quality electron-beam image, the method in which producingefficiency in a process of producing a substrate having a circuitpattern formed from an electrically conductive or electricallynon-conductive material such as a semiconductor device, a mask, a liquidcrystal, etc. is improved by executing the circuit pattern inspectionaccording to the present invention, and so on, an inspection method andan inspection apparatus obtained by any combining a plurality ofcharacteristics described in claims can be made without departing fromthe scope of the present invention.

Typical effects obtained by the preset invention will be described belowin brief.

Inspection of a circuit pattern formed from a silicon oxide film, or aresist film which was so light-transmissible as to be unable to bedetected by conventional optical pattern inspection could be achieved byinspecting a substrate such as a semiconductor device, or the like,having a circuit pattern by using a circuit pattern inspection apparatusaccording to the present invention. Furthermore, a circuit patternhaving an electrically insulating material from which a stable image ishardly obtained in the conventional SEM can be inspected in aninspection time which can be put into practical use in a method ofproducing a semiconductor device, or the like.

Because defects which cannot be detected by the convectional technique,that is, abnormality in production apparatuses, conditions, etc. can bedetected in an early stage with a high accuracy by applying thisinspection to a substrate producing process, a measure counter to theabnormality can be given to the substrate producing process immediately.As a result, the percentage of defects in the semiconductor device andother substrates can be reduced so that producing efficiency can beimproved. Further, because the occurrence of abnormality can be detectedquickly by applying the aforementioned inspection, the occurrence of alarge quantity of failures can be prevented. Further, because theoccurrence of failures per se can be reduced as a result, reliability ofthe semiconductor device, etc. can be improved so that not onlyefficiency in development of novel products, or the like, can beimproved but also the cost for production can be reduced.

1. A sample inspection apparatus comprising: a sample stage to which asample to be inspected is mounted; a first electron beam optical systemfor irradiating a primary electron beam to the sample; a deflector toscan the primary electron beam on the sample; a power supply to apply apotential for deceleration voltage to the primary election beam; adetector for detecting secondary electrons generated from the sample andfor outputting a signal of the detection; a second beam source toirradiate a second beam to the sample; wherein an energy of the primaryelectron beam is controlled so that the ratio of the number of electronsincident to the sample and the secondary electrons emitted from thesample are made to be substantially equal.
 2. A sample inspectionapparatus according to claim 1, wherein the second beam source isarranged in a different position from an optical axis of the electronbeam optical system.
 3. A sample inspection apparatus according to claim1, wherein a size of the second beam is larger than that of the primaryelectron beam.
 4. A sample inspection apparatus according to claim 1,wherein the second beam source is an electron beam source or an ion beamsource.
 5. A sample inspection apparatus according to claim 4, wherein acurrent density of the second beam is smaller than that of the primaryelectron beam from the electron beam.
 6. A sample inspection apparatuscomprising: a first electron source for generating a primary beam; afirst electron beam optical system for converging the primary electronbeam; a sample table for mounting a sample thereon; a deflector formaking the converged electron beam performs scanning on the sample onwhich a circuit pattern is formed; a power supply through which anegative voltage is applied to the sample table or the sample; adetector for detecting secondary charged particles generated secondaryfrom the sample; a second charged particle source which generates asecond charged particle beam for electrically charging the sample; asecond charged particle beam optical system for converging the secondcharged particle beam; a sub chamber holding the second charged particlesource and second charged particle beam optical system; and a substratecarrying system for carrying to the sub chamber; wherein the secondcharged particle beam is irradiated onto a region to be inspected in thesample before irradiation the primary electron beam.
 7. A sampleinspection apparatus according to claim 6, wherein the primary electronbeam inspects another sample while irradiating the second chargedparticle beam at the sample in the sub chamber.